# Battery capacity testing with Imax B6 charger



## kmjelle (Nov 29, 2007)

When charging and and discharging li-ion and lipo packs the display tells you how many mAh was put into the pack. I guess the battery don`t store all the energy. When discharging you also get a mAh number. Can this last number be trusted as the true capacity of the battery?


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## MtbMacgyver (Jan 23, 2007)

Charging is not 100% efficient, so the number that goes in on the charge will typically be higher than the capacity. How much higher depends on factors such as the charge rate. 

For Ni based batteries, the charge is quite inefficient and the batteries often get pretty warm. The excess energy during charge is mostly turned into heat. For Ni batteries the charge mah can be as much as 30-50% more than the battery capacity. 

Li based batteries charge much more efficiently and hence do not get very warm on charge. Typical mah input on the charge will only be around 5-15% higher.

The reading you see on discharge, assuming the charger is measuring the number accurately, is the true capacity at the discharge rate of the test. Again, how close that is to the spec will depend on many factors such as discharge rate. The spec is typically defined at a 10 hour discharge rate and in ideal lab conditions. If you're running the battery down faster than 10 hours, the number is going to be lower. Age also matters. You're at the mercy of the battery supplier in terms of how well they manage their inventory and how long the cells or packs have been sitting on a shelf.

The best I've ever seen at the actual discharge of rate of my lights (700ma) is 2500mah out of 2600mah Sanyo cells. The worst I've seen is 1200mah out of cells that were marked as 2800mah from ebay. They were clearly seconds, likely old, and probably with an exaggerated initial spec. I just measured a batteryspace 2400mah pack made with LG cells that I've had for 5 years now. It measured 2150mah which I think is pretty good considering the age and usage. That's only down 50mah from when I got the pack 5 years ago.


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## yetibetty (Dec 24, 2007)

I don't have an Imax B6 but do have use a GT Power A6 charger and assume both chargers are similar and yes I trust mine.

I only check how much was put back in and you must renember the the quoted ma for a cell or pack is from fully discharged to full, you will not fully discharge a pack or cell as it will be destoyed so expect a bit less than quoted.

I have an old 4 cell pack that could be up to four years old that started out as 2400ma and according to my charger is now down to 2050ma and is on par with what MtbMacgyver has found.

At least think of it as a very good indication of battery capacity.


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