Sealed lead acid battery

[alan_m]

I have a multi-light rechargeable torch that takes a sealed lead acid battery (6V, 4Ah).

I had occasion to use it recently and found the battery to be somewhat dead. It operated the light for a very short period before the terminal voltage began to fall rapidly.

I have purchased a new battery but what is the best way of maintaining it in reasonable condition? I suspect that the charging circuit within the torch is no more sophisticated than just maintaining a trickle charge. The torch itself (with its own internal charger) will be sitting virtually forgotten for perhaps a year just plugged into a mains socket.

I could put it on a timer so that it (trickle) charges for a short period during each week. I could also add a small load so it discharges slightly during periods when it isn?t charging. Would either of these make any difference to the longevity of the battery in maintaining its nominal capacity?

[harry]

d-batteries/

[Harry Bloomfield]

alan_m brought next idea :

In my garage I have a series of sockets which switch on for 1 hour per day. Into those sockets I plug several chargers which includes the charger for a 10" portable lamp with a sealed l/a inside it. That l/a battery recently failed after this having this treatment for the past

10 years. Deliberately discharging to recharge is a bad idea, as I believe also is being on a constant charge.

[Rob Morley]

First check that it's trickle charging at the optimal voltage (about

6.8V for a nominally 6V lead/acid battery).

[T i m]

Ok.

Yes, if you got one of those plug-in timers where you could override it for say 24 hours, but have it set to come on say once a month otherwise for 15 mins (possibly tested by trial and error with a DMM on battery whilst charging if possible).

The idea is if you actually use it, you put it back on charge and 'override' the 'Off' timer and it would then charge for 24 hours before automatically reverting to it's 'maintain' cycle.

I wouldn't. 'Cycling' a LA battery doesn't improve it's performance (after the initial cycles etc) and all adds up to exhausting it's life etc.

Yes, I think it would, given the 'dumbness' of most of the chargers that come with such things and depending on you actually using the torch for a reasonable time once in a while (but not over-discharging it either). Remember, a lead acid battery is normally considered fully discharged at 50% of it's nominal capacity so assuming it doesn't already have a Low Voltage Disconnect, you could measure the running current (DMM again) and work the running time out from there (allowing for degradation over time etc). eg, if it's a 4Ah battery, real world

2Ah, if the light draws .5A then that would give around 4 hours constant use (if pushing the battery to it's limits), so 3 or even 2 hours might be better, *not* till the light goes out! ;-)

Cheers, T i m

[Graham.]

Check Vent Caps: Not applicable to SLA batteries Harry.

Clean The Terminals: OK

Check Connections: OK

Check Electrolyte Levels: Not applicable to SLA batteries Harry.

Add Water: Not applicable to SLA batteries Harry.

Perform an Equalization Charge: Most definitely not applicable to SLA batteries Harry.

2/6 See Me.

[Brian Gaff]

Yes I had a Grundig cassette radio withed a 6v dryfit in it and it did not last as long as I had hoped. The charger in the radio seemed to contain 1 transistor and a couple of resistors connected to the internal transformer so not exactly sophistication city either.

Brian

[Dave Plowman (News)]

A lead acid battery self discharges very slowly. So there is no need to float charge it - unless it is being discharged by the electronics in the device. 6 months wouldn't harm a battery which was left in a fully charged state.

What does harm then is over-charging. Which some poorly designed chargers might well do.

I'd check the voltage at the battery when fully charged and still on charge. If that exceeds 6.9v, it's not a well designed charger.

[Max Demian]

I've had a Vax hand held vacuum cleaner with a 6V lead acid battery for over five years and it still keeps its charge very well...

[Dave Plowman (News)]

I've got a Lidl car jump start pack that includes a compressor. Bought long before Lidl branches were everywhere. Well over 10 years old, and still holds enough charge to top up all my tyres a few times before needing charging. It was half the price of the same branded item in Halfords. Quite the longest lasting lead acid I've ever had - even if now likely past its best.

[Chris Green]

Around 5%/month, hardly 'slow'.

After 6 months it will be somewhere around 25% discharged which I suppose is OK but you'd be better off (as regards battery life) by keeping it more fully charged.

Also true of course, a good lead acid battery charger will drop back to float voltage when the battery is fully charged and a really good one will have a temperature sensor (float voltage varies with temperature) *and* have different settings for different battery technologies.

[Harry Bloomfield]

Dave Plowman (News) explained on 18/01/2018 :

Likewise, but from Aldi and likely 15 years old. It's charger is on my garage circuit which turns on for one hour per day, which I mentioned below...

[T i m]

It can depend on the battery though. The one the OP bought is a bit under the 5%/m at 3%:

And the one I replaced in Mums alarm the other day says it can be safely left uncharged for a year.

As you say, it wouldn't do any harm but not ideal ...

Quite.

But this is the one that comes with a torch so probably just a full wave rectified transformer wall wart, hopefully with a peak output voltage less than 13.65V and a current of less than one amp. ;-)

I still think a good compromise solution is to plug it into a 30 day timer and have it coming on for a couple of hours once a month or so but with the option to override the timer for 24 hours and have it automatically reset once 24 hours were up.

You start off with a full 24 hour charge and then it just gets a topup every 30 days to replenish the 3% (.12Ah?) it's lost to self discharge.

If it's used, especially for any length of time you just override the timer and it get's a full charge again.

Cheers, T i m