What is the Ideal point to start Recharge on NiMH (Eneloops in particular)

[matrixshaman]

Having just got some new Eneloops NiMH AA (thanks to coppertrail) I realized the only NiMH I've had in the past rarely got used and I didn't really know when they should get a charge (I used NiCD's for quite a while but that's a different beast). What I'm asking is at what voltage would it be best to recharge an Eneloop? I'm always close to a meter and a charger and I don't need to use these for extended time runs so I can check and track how much charge they have left often with ease. I'd like to know how to best keep these healthy. I've seen Silverfox mention NiMH should be fully discharged every 30-50 cycles but also wonder if this also applies to the slightly different Eneloop chemistry. So should these just be run down to around 1.0 volt or more or less before charging? Or maybe just charge when they drop out of regulation or start kicking down fast in a regulated light? Any input appreciated. I'm guessing this may have been answered here before but I didn't see it in the 'Sticky' and I'm not sure how to do a search here for this as CPF's server doesn't seem to like multi-word searches and the Google search only produced 1 hit and that was irrelevant.

 

[SilverFox]

Hello Matrixshaman,

A very interesting question...

Cycle testing involves a 60% depth of discharge for 48 cycles, followed by a complete discharge on the 50th cycle. Cells are supposed to be able to handle over 500 cycles of this.

Manufacturers suggest that a cell can handle more shallow cycles, than 100% discharges. This suggests that there would be some benefit in charging more frequently.

I just ran a quick check and if your cell is reading around 1.22 volts resting, it has around 50% left. So, you could try recharging when your cells get in the 1.20 - 1.22 volt range and see how that works out.

Tom

 

[LuxLuthor]

Wouldn't it be nice if manufacturers gave ideal battery care for their product....especially when a new one like this comes out? They leave the average consumer to stumble blindly in the night, where in reality they likely know exactly how enthusiasts should treat them.

 

[WildChild]

They are cheap! If they die replace them! (This is how manufacturers think...) On my side, I just try to not over-discharge them! I usually top them off if I am to need batteries for long runtimes. I also charge them either in the Energizer 15 minutes charger or the Costco's Sanyo 1h charger. If I get over 100 cycles from them I'll be happy and if they dies before with high self-discharge, I'll try to get them replaced by the manufacturer for free (defective ones). I've done that a few times with faulty Energizer or Duracell.

Wouldn't it be nice if manufacturers gave ideal battery care for their product....especially when a new one like this comes out? They leave the average consumer to stumble blindly in the night, where in reality they likely know exactly how enthusiasts should treat them.

 

[matrixshaman]

Thanks Silverfox - 1.2v sounds like a point to use . Eneloops came out of the package at 1.309 volts on the Fluke and with a fair amount of use in a AA LED light my first one is still a little over 1.28 volts. Eventually I will get a ZTS battery tester but for now I tend to rely on the no load voltage as a rough reference of the charge level. At some point I plan on building a custom charger (probably a pulse charger) for all my batteries. I've built variable power supplies from scratch in the past and unless I find a charger that does everything I want I'd rather build my own. Based on what I've seen in a brief search chargers currently available are not able to do everything I'd want in a charger. One thing I'd need is complete shutdown of the charge function when a battery reaches an exact point you choose to set for it (such as 4.20 volts for Li-ion) and ability to control charge current - also able to charge NiMH and Li-ions.