Determine True Rechagable Battery Capacity - Page 1
Forum section: electronics / general

author: cosmarchy
author_rank: Contributor
timestamp: October 05, 2025, 09:44:21 pm
content: Hi,I have a number of NiMH rechargeable batteries all from different manufacturers and all different capacities.I charge them with a XTAR VC4 charger and pretty much all of the batteries show as well below their rated capacities even when charged for the first time.I wouldn't have said any of the batteries were from cheap no-name manufacturers; they are all reasonable quality brands so wouldn't think they were dodgy.Does anyone have any similar experience when using an XTAR VC4? I'm trying to determine whether it is likely the charger not charging properly or the batteries really are knackered.If I end up getting another charger, can anyone recommend one they use which has been reliable? I basically want to charge 18650 Li-ion, AA and AAA.Thanks

author: RoGeorge
author_rank: Super Contributor
timestamp: October 06, 2025, 09:34:06 pm
content: Don't know about the charger, but NiMH have to be cycled 5-10 times when brand new. They reach their nominal capacity only after a few full charge/discharge cycles. Usually this is mentioned in the datasheet, or in the battery user guide/flyer, if there is any.

author: cosmarchy
author_rank: Contributor
timestamp: October 07, 2025, 07:16:56 pm
content: Ah,Wasn't aware of that, certainly nothing in the datasheets accompanying them.I'll have to give them a few charges and see if the reported capacity changes.Thanks

author: kite31
author_rank: Regular Contributor
timestamp: October 08, 2025, 05:23:59 am
content: I am unconvinced by my Xtar VC4. I use it for 18650 cells which it seems to do OK, that being a simple program. I have tried it just once on NiMH wgere it generated excessive battery heat compared with my older iCharger 1010B+ which is very efficient with Nickel chemistries.

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: October 08, 2025, 10:43:11 pm
content: Also make sure your discharge current is the same as the datasheet's. The usable capacity will drop rapidly at higher discharge currents.

author: makebit
author_rank: Unknown
timestamp: October 15, 2025, 10:16:28 am
content: Basically you should make up your own charger on a bit of stripbpard, using a linear current regulator to charge the cell off say a 9V wall wart output....(or 5v).You will have a current sense resistor in there so you can see if you are overcurrenting it or not.Add a comparator or whatnot to stop charging at xx Volts...In fact, rather than a comparator, you can use an opamp integrator as an accurate charge-cut-off trip. That way you dont need to mess about with a comparator with hysteresis.An opamp integrator is often a good substitute for a comparator when you dont need lightning fast tripping.Then put that cell on a discharge load eg some resistors, or a known current sink made up of an opamp and transistor.That way you get a charger into which you can get into its raw guts and really see how its working.And compare the result with your charger.No need to add taper charging finish-up in the first instance.

author: kite31
author_rank: Regular Contributor
timestamp: October 15, 2025, 11:08:53 am
content: You could look on the second hand market for one of the fancy NiCd/NiMH chargers made back at the beginning of this century for flight or RC cars. While there are corresponding American chargers whose names I no longer recall, something like a Schulze Eco or Orbit microLader have more ways of charging and discharging a nickel chemistry battery than you thought could exist. Those companies are out of business since cheaper units like the iCharger turned up. Today I saw a Supernova 250S going for $25 in the US, another excellent nickel charger that will also charge your Pb battery. These units are designed for fast charge/discharge between races but will go very slowly if you want.