Maintenance Question - NiMh Batteries

[TheAce]

Hi evevrybody,

I bought a new torch, Sepadiver 50 - An excellent light, very very bright with rechargeable Nimh batteries.

http://www.sepadiver.com/CATALOGO/torce/PAGINA 49.htm

I have a question for all of you who understand and know about batteries and battery maintenance.

In the manual it is recomended to discharge the light completly and recharge it full to prolong the life of the battery and to keep it in top performance. They also recommend to charge it right before using so to have max power.

The light has an electronic circuit that shuts the light off before the battery drains completely.

My question is:

I dive every weekend, what would you do?

1) Would you drain the light empty after the dive and charge it full immediatly (so I don't leave it discharged for a week which I understand is not healthy for NiMh batteries) and use it only the next weekend? (will it discharge by itself and won't give me full performance?)

or

2) Would you drain the battery after the dive till the circuit shuts the light off, leave it discharged for a week and charge it full the next weekend before the dive?

or

3) To leave it as it is and the next weekend before the dive discharge it and then charge it full?

I hope you undertand my question... if I wasn't so clear please let me know...

By the way, if it is important or not, in the manual it is recommended to charge the batteries for 14 hours if the light is completly drained. They recommend to charge it for 16 hours if it hasn't been used for over 2 months. The charger does not seem to have a timer circuit. And the battery becomes hot after about 10 - 11 hours.

Thanks for trying to help...

 

[Goeduck]

Here is an excellent web-site that can answer all your questions about NiMh batteries, including charging, using and storing.

Hope this helps.

Goeduck

 

[TheAce]

So, if I understood right, the best option would be No.2 (Discharge it after the dive and charge it full the next weekend before the next dive)? But won't it hurt the batteries to be discharged for a week?

And by the way, someone knows/has this torch?

 

[TheAce]

No one knows this torch? No one knows about rechargeable batteries?

 

[fgray1]

Sounds to me as if the instuctions are for Nicad Batteries.
Nimh don't hold memory and its not good to drain them completely. they have the same curve as Gel cell bateries.
They drain slowly in the begining of use but after a while they drain quikly.
Your surpose to simply recharge the batteries to full charge then place in storage charged and top off the night before there use to make sure they are fully charged.
Hope that helps.
Fred

 

[DarkFrog]

When I got NiMH batteries I did a bit of research. The manufacturer of my batteries implied that near complete discharges every once in a while could be good for the battery but was more pain then its worth. Completely discharging the battery destroys it.

I only use mine for my Gameboy and my GPS, so I just wait until the device turns itself off and then I know its time to recharge the battery, but with lights its a bit trickier. I'd probably do what fgray1 suggested and just top them off before diving.

Another thing to keep in mind is that fully charged NiMH will lose about 40% of their charge if left at room temp. for a month. I charge mine immediately and then store them in the freezer between uses.

 

[Genesis]

are not bad for NiMH cells.

However, even SLIGHT reverse-charges will destroy them. The problem with fully discharging a pack of them is that when the first is fully discharged the rest are not (there is always some level of discrepancy in capacity) which reverse-charges the "dead" cell and ruins it.

The best practice is to fully charge the pack no more than one day before use. Even better if you can individually charge each cell. This is one reason its a good idea to let a pack self-discharge to "zero" once in a while - it avoids the disparity in cell capacities being multiplied and eventual overcharging of the "strong" cells (which also damage them), along with avoiding the risk of a reverse-charge of one or more cells if you discharge them under load.

Unfortunately the practice of welding cells together into packs makes truly proper charging impossible. What SHOULD be done is to build packs out of individual "button cells" and charge them in a charger that can individually monitor and charge EACH cell.

If I change over my Pro 6 cannister to a NiMH pack (or build a new cannister to replace that one) I will definitely address this by figuring out some way to build a holder that will allow the use of button cells and arrange them in the proper series/parallel arrangement to get the capacity and voltage I want, but allow individual cell charging.

 

[ScubaAaron]

After diving, when the batteries are approx 1/2 discharged, is it best to:

(1) leave them in this partially discharged state until a day before your next dive when you recharge to full

or

(2) charge them now as well as one day before your next dive

In other words is it acceptable to store them partially discharged [option (1)]? I would reason that it IS acceptable as even if you fully charge them they will soon be partially discharged as they self-discharge... plus the fact that in option (2) you are in effect charging them twice between dives and thus "using up" the charging cycle life of the batteries.

Are my assumtions correct?

 

[Genesis]

Sealed LA cells should NEVER be permitted to fully discharge. They will be ruined if you do, as the plates sulfate and then you're hosed. You want to store a SLA battery fully charged.

NiMH cells CAN be permitted to fully discharge, but NEVER reverse-charge. The problem is that doing the first is impossible with the cells in a pack under load. However, SELF discharge is just fine, and, in fact, is preferred, as it "resets" the differences between cells which otherwise exist. NiMH cells have no problem with being partially charged, fully charged or fully discharged; the problem with them is that if you continually charge/part-discharge you will eventually end up with one cell that is massively different in its charge state than the others, which will eventually ruin one or more cells - either one will get reverse-charged during a cycle, or the others will be OVERcharged and boiled. Either trashes the pack.

So, if NiMH, leave them alone until a day before the next dive.

If SLA, then recharge immediately.