eneloop rechargeable AAA Question

[Bertie Doe]

On recs from this group, I bought eneloops AAs for our Braun toothbrushes and they're great i.e. 8 to 10 weeks between charging (s) and loadsa oomph.

I've recently bought 4 x AAAs to power a hand-held unit for a fishing gadget (££ ouch).

Question is, should these high-end AAA batteries be 'topped up' or will they develop a memory? Thanks in anticipation.

[Martin Brown]

They don't like being left totally discharged for long periods and they don't like being overcharged either. Anything in between is fine. I only recharge when they are flat and carry some spare single use cells.

If they are low self discharge types they are ideal for low current long term use and can be used out of the pack. They will last longer when starting from a fully charged state but not by all that much unless they have been on the shelf for years prior to purchase.

Memory effect was a big problem in the previous NiCd era with the cells deteriorating rapidly when SOP for charging rugged almost indestructible NiFe cells was applied to them. MOD trashed a lot of new batteries.

[Bertie Doe]

Thanks Martin, I should have mentioned that I have 2 chargers. One charges AAA in 1 hour and AA in 2 hours. The other charges AAA in 6 hours and AA in

13 hours. (Quick versus Trickle).

Both chargers have a 'Discharge' feature, so I guess it's there for a reason. The paperwork that came with them, is long gone.

So the question is - what's best for battery longevity :-

1. Top them up
2. Hit the Discharge button
3. Transfer the batteries to say, a torch and let them slowly discharge overnight. TIA.

[Max Demian]

It's really only the old NiCad cells that suffer 'memory effect'. NiMH are fine to top up.

[Bertie Doe]

Ah thanks Max, I wasn't aware of that. Looking thru' my stash, even my elderly Energizers are NiMH.

[Martin Brown]

It mainly dates from the NiCad era. They really did have very bad memory problems.

Once they are down to 10% or less is my working solution.

Probably not necessary. The thing that might do for them is keep charging them again and again from 90% to 100% on a dumb charger.

Will discharge them to a state where recharging may become impossible. (in the case of Lithium ion batteries potentially a fire hazard too)

It is a bad idea to take the terminal voltage of a rechargeable battery much below 1v if you want to maximise their lifetime.

Somewhat out of date but otherwise OK summary by TI here:

Modern NiMH have much lower self discharge rates.

[Bertie Doe]

Thanks Martin, saved to favs and also a good read :-

"Sustained high-current overcharge and cell polarity reversal (during discharge) are the main killers of Ni-Cd and Ni-MH batteries:"

I think I'll stick with the trickle-charger mentioned earlier.

Some humour ref Li-ion pyrotechnics :-

"The makers of Li-Ion cells handle the explosion threat by designing the case of the cell so that it will "die with honor", and not explode in someones pants pocket if the battery hits their car keys. More important, the actual battery terminals are simply never allowed to reach the outside world."

[tabbypurr]

Sounds like a good way to halve their life. They only have so many charge cycles in them, wasting 50% isn't going to help you.

NT