[Larrymc]

Yes.
- Fully discharge a battery by using it or leaving the camera switched on until the camera indicated "Battery depleted" and switched off

- Fully charge a battery
- Insert the battery in your camera
- Set the camera auto power-down to "Off"
- Note time of the day
- Wait until the camera display "Battery depleted"
- Note time of the day, calculate how many hours the camera stayed in standby mode.

Do this for each battery you own, note the difference of how long it takes for each battery from fully charged to fully depleted.

Why go to all that trouble calculating how long a battery is going to last? Why not just carry a couple of fully charged batteries with you when you are out shooting? When the camera battery indicator gets toward low change batteries. Even OEM batteries aren't all that expensive.

[James also]

Never retain an old battery.

Retain the battery till it will not hold enough charge to last as long as you would like. On a busy day I would take 250-400 photos an older battery will handle that with few problems. Even the no name versions. If you are going to take over 2000 photos in a session on a regular basis then you will need to replace the older battery. I hardly ever use live view which helps.

[Bison Bud]

The only way that battery capacity can be measured is under load! One could calculate an acceptable fixed resistance load by using Ohm's Law and solving for current, then put an ammeter in line with the circuit to monitor and time the discharge to calculate the Ampere/Hour capacity. However, I would not recommended this as these tests can be very hard on the battery due to the increased heat and the simple fact that this would be just one more charge/discharge cycle in the battery's overall lifetime performance (they all cycle only so many times and do wear out). Anyway as others have mentioned, a static voltage measurement does not indicate battery capacity. However, since most batteries are made up of multiple cells (the actual definition of a battery), a voltage measurement can show a weak or dead cell, which will keep the battery from fully charging and is generally the kiss of death for any battery pack.

My recommendation for maximum battery life would be to charge your batteries carefully, hopefully with a peak sensing charger, and hopefully being very careful not to charge too quickly, overcharge, or generate any real heat. Otherwise, I think decreased performance should be pretty noticeable and testing will probably only add to the problem. Good luck and good shooting to all.

[James also]

My recommendation for maximum battery life would be to charge your batteries carefully, hopefully with a peak sensing charger, and hopefully being very careful not to charge too quickly, overcharge, or generate any real heat. Otherwise, I think decreased performance should be pretty noticeable and testing will probably only add to the problem. Good luck and good shooting to all.

The sharp start trickle chargers definitely the best. Sometimes means an overnight charge but the results are good.

[marcusBMG]

I think the essentials of chargers is more straightforward: it must supply a sufficient voltage, appropriate ampage and it must measure when the battery is fully charged.

Batteries are more tricksie. i've been shopping around for Li Ion 18650's to rebuild a battery for a drill. From browsing u-tube (there's loads on this) it's clear that the market is awash with fakes, recycled batteries sold as new and simply low quality ones. Without testing equipment to measure load capacity etc you'll only get an impression of what you've got from usage. sample video:

You Tube

You Tube

This was my review of an Ansmann DLi90

What's the difference between a generic D-Li90 and a pentax D-Li90, particularly since they both have made in China on the back? Same chems inside, plastic case, circuit board, emanating from some manufactory in the east. Well, if you've ever tried some real cheapo cells, as I have, then you may have found, as I did, that treating items like this as a commodity may not work. After a few months half of that job lot of rechargeable AAA's had already been binned!
However the no-name generic D-Li90 battery I acquired off ebay 3 years ago has done well enough. It's still going ok, it was the original Pentax one that began to really lose its capacity to hold charge - that was at least a couple of years older mind you.
I did quite a bit of browsing pondering the dilemma. One thing was sure: the pentax own labels at £60 odd were way OTT price wise. Sorry pentax but no deal. ....
In a commodities market where it is next to impossible from the outside to distinguish the good from the rubbish and the price differences have an arbitrary or profiteering character, a trustworthy brand name that reassures as to quality can pay dividends. ...

[RGlasel]

Why go to all that trouble calculating how long a battery is going to last?

Good point. I think there is a tendency to overthink this stuff. I've never had a camera battery suddenly fail without warning, after working flawlessly for the previous several months, but a single battery of any type can not be counted on to work properly in critical situations. If battery power is essential, you have to have backups. Even my $200 implant batteries are only warranteed for 3 months; if I can't afford to be deaf if the output voltage of the battery I'm wearing drops slightly, then I take backups with me. Even then, I've had problems with the contacts on the implant and trying all 4 batteries didn't help. Stuff happens. If a cheap third party, aftermarket battery purchased on eBay or Amazon from a vendor on another continent doesn't do what you want it to, buy better batteries next time. Buying OEM is not a guarantee you are getting the best on the market, but the manufacturer of a $1000 camera isn't going to stick with a battery vendor that hurts the reputation of the camera, so if all else fails (or you aren't likely to ever buy another camera battery), buy OEM.

[Penview52]

Retain the battery till it will not hold enough charge to last as long as you would like. On a busy day I would take 250-400 photos an older battery will handle that with few problems. Even the no name versions. If you are going to take over 2000 photos in a session on a regular basis then you will need to replace the older battery. I hardly ever use live view which helps.

Old batteries are toxic and hazardous to environment, if you have retained car batteries in your backyard - dispose it. Lithium batteries that are over charged have tendency to explode and oxidation fumes will hurt human health. Newer batteries takes more pictures as compared to old batteries but bear in mind that all stuff have useful life span. I am not rushing to my conclusion but saving in a wrong way is bad idea. Deteriorating battery charge will affect the performance of the camera until such the camera will deteriorate also.

[DeadJohn]

I suggest recording a movie because that's a relatively fast battery drainer, and doesn't wear out the mechanical shutter like taking thousands of still photos. Set the camera to the lowest resolution video mode so you don't fill the card too soon. If the first movie reaches the hard limit for one file (25 minutes?), start a new movie and add up the total time.


You could rig up a battery tester with a resistor or light bulb. Start with a fully charged battery, connect your test rig, measure how long it takes to discharge the battery. There's a risk of shorting the battery and ruining it if you do things wrong.

[GUB]

You could rig up a battery tester with a resistor or light bulb. Start with a fully charged battery, connect your test rig, measure how long it takes to discharge the battery.

I have done this with AA rechargeables -- but put a cheap battery analogue clock in parallel with the light bulb. Start the clock at 12 and come back at your leisure to see how long it ran for.

[Fluegel]

Battery capacity is given in discharge current against time.
I could not find actual figures on the battery used in Pentax cameras.
My estimate is these batteries supply about 500 mA for one hour, or as the rule of power say 250 mA during 2 hours.
Tragically this figure does not help us much because a camera does not discharge the battery with a steady current.
Discharge depends on using life view, recording video, recording sound etc.

If you want to compare the actual capacity of several batteries you could use the procedure in post 11.
Another possibility is to discharge fully charges batteries with a small bulb and look how long the bulb gives a steady amount of light.
You guys are clever enough to think of a device that registers hours of the lamp emitting light, i do not have to describe that.

A steady discharge is in no way helpfull to predict how long a camera can be operated with a battery.
The K5ii I use came with three OEM batteries, one was partly discharged and is still in the camera after being fully charged.
The other two I also charged, both give full power after a month rest when being fitted to the body.

Bad batteries may initially indicate fully charged but will loose power after 10-40 shots.

For those who own a multimeter: measure the voltage of the battery. Find a small bulb that will draw about 50 mA connect the bulb to the battery and watch how long the bulb gives a steady amount of light.
I suppose all chargers calculate current against charging voltage to decide when to cut off the charging of the battery.

To sum it up:

You can check the actual capacity of batteries and compare the figures for the batteries tested.
The capacity measured will tell you which battery stores the largest amout of energy.
Because the power consumption of the camera is not a steady current it does not give you an indication of the hours the camera can be operated.

[AstroDave]

You could rig up a battery tester with a resistor or light bulb. Start with a fully charged battery, connect your test rig, measure how long it takes to discharge the battery. There's a risk of shorting the battery and ruining it if you do things wrong.

I'm working on it!

At the moment, I am measuring voltage versus time for charging a D-LI90 (genuine Pentax, but around 6 years old). I haven't tried measuring the charging current. I made a special holder which gives me access to the battery terminals while charging.

When the Pentax charger thinks it is fully charged, I'll measure the discharge versus time using a resistor. By monitoring the voltage across the resistor, I will also get the discharge current current as a function of time. I contemplate discharging at around 0.1 C . As noted by folks above, this is not quite the same as normal camera usage, which tends to make fairly heavy but quite intermittent current demands. But, I should still have a feel for behavior of a rather old battery. If there are some wacky results, I can also test against a newer (but still ~3 year old) Pentax battery.

I'm not too worried about wearing out the battery - various reputable places on the web suggest thousands of charge/discharge cycles for Li batteries. Look at the last plot in this presentation: Battery Performance Characteristics - How to specify and test a battery (an overall good discussion of some of the issues in this thread)

Correction: it's the 3-year old battery that is currently under test. The 6-year was already fully charged. I'll measure the discharge curve for it, too.

[James also]

At the moment, I am measuring voltage versus time for charging a D-LI90 (genuine Pentax, but around 6 years old). I haven't tried measuring the charging current. I made a special holder which gives me access to the battery terminals while charging.

I'm looking forward to your results.

I have 5 DLi90 batteries varying between 3 and more than 10 years old. I wouldn't know which is which.

Funny isn't it at work I diligently test hundreds of batteries on an eight week cycle monitoring results. At home not even a purchase date is on the batteries.

[AstroDave]

At home not even a purchase date is on the batteries.

Are they real Pentax? Those have a month/year code on them.

[biz-engineer]

Why not just carry a couple of fully charged batteries with you when you are out shooting?

Because I don't want to carry a spare weak battery fully charged that suddenly drops to 50 shots capacity because it's -15C outside in winter?

[James also]

Are they real Pentax? Those have a month/year code on them.

I have 3 genuine pentax batteries one has 201401 printed on it and the Ricoh brand. the other 2 have no date but the Hoya branding so probs years old. The 2 no name batteries have no date on them either.

I have never really looked at the batteries before but the Pentax brands are 7.2V 1860mAh and the no name are 7.4V 2000mAh.

The Pentax charger output is at 8.4V so it shouldn't be a problem