Bongo Fury

Drove all the way down to Chamonix with my coolbox running, not realising that the inline fuse on the LB charging lead had blown. Then I left it running for a further couple of hours after parking up. The battery is now showing 7.5 Volts! Have I done it irreparable harm? It's on 2 amp trickle charge at the moment so it's going to be a day or two before I know if it's taken/held the charge or not.

TerryG wrote:Drove all the way down to Chamonix with my coolbox running, not realising that the inline fuse on the LB charging lead had blown. Then I left it running for a further couple of hours after parking up. The battery is now showing 7.5 Volts! Have I done it irreparable harm? It's on 2 amp trickle charge at the moment so it's going to be a day or two before I know if it's taken/held the charge or not.

I'm afraid I did that to my Numax LB. It was never the same after that. Sorry to be the bearer of bad news etc. After that I fitted a voltmeter, so I could check that the voltage jumped up after starting the engine (meaning the alternator had - via the voltage sensing relay - started throwing its charge across to the LB, indicating that the fuse was intact).

I'm seriously thinking of fitting a master low voltage protector to the LB just so nothing can drain it to the point of damaging it (cost about £40 on ebay - you can get cheaper things but they don't handle the amps).

At a 2Amp trickle charge its going to take quite a while to get back up, assuming its about 85AmpHr then at 2 Amps its going to need 48 hours at least and then it will only be to about 70%, can you not borrow a larger charger or replace the fuse and go for a LONG drive! You may not have done serious damage, provided you can recharge it again pretty quickly and provided it isn't allowed to gas at all, if its not a sealed battery check the levels and top up with distilled water if at all possible.

Isn't the point of a leisure battery to be able to run it down and charge it again?

westonwarrior wrote:Isn't the point of a leisure battery to be able to run it down and charge it again?

In theory, according to some sources, but I've read time and again they don't ACTUALLY like being run dead flat (and left that way for days ). Best avoided I think and anyway what practical use is it doing that so better safe than sorry?

westonwarrior wrote:Isn't the point of a leisure battery to be able to run it down and charge it again?

Yes but there is running it down and running it right down.

If you are going to flatten a battery that much it has to be a deep cycle battery, not just a "leisure" battery which is just an ordinary battery that is supposedly slightly more tolerant of discharge than normal.

My point being they are supposed to be able to run down if parked over a few days camping then charged, thats what they are made to do like in caravans etc

and thats why they are different to starter batterys

I know they should not be run down beyond 50% even though some state they are made to.

http://en.wikipedia.org/wiki/Deep_cycle_battery

I'm confused as 7.5 volt is not 50% of 12.6 ,,, I'm sure I am missing something here

scanner posted while I was typing and answers my ? a little I thought all were deep cycle

westonwarrior wrote:My point being they are supposed to be able to run down if parked over a few days camping then charged, thats what they are made to do like in caravans etc

and thats why they are different to starter batterys

I know they should not be run down beyond 50% even though some state they are made to.

http://en.wikipedia.org/wiki/Deep_cycle_battery

I'm confused as 7.5 volt is not 50% of 12.6 ,,, I'm sure I am missing something here

scanner posted while I was typing and answers my ? a little I thought all were deep cycle

The 50% bit isn't measured in volts SFAIK, it's something to do with the amp hours bit and that isn't what the volts measure.
To a 12v battery 10 volts is flat, 7.5volts is very very flat.

If a good leisure battery were to cost you £100, a half decent, equivalent capacity, deep cycle battery would, at the very least, be £250-300.

ahhh ty

I never could get my head round this amps volts thing

So I just bought and am about to fit a new leisure battery which was bought as a marine / caravan deepcycle battery and was a bit worried I may fry it if I rely on it too much

There is a lot of misunderstanding going on here!

Lead Acid batteries are ALL pretty rugged. However they can be tweaked to give a better life depending on how they are to be used.

Starter Batteries - They need to be able to supply several hundreds of Amps for a few seconds, so they need physically strong and thick lead plates to enable the current to flow without dropping too many volts (plus several other factors but that is the main one).

Leisure Batteries - They need to have the have a high capacity, but are only expected to supply a few tens of Amps at worse over long periods, so they have quite thin plates to get the maximum surface area whilst not taking up to much room so that more plates can be accommodated, often these days the lead is supported on Glass Fibre structures giving more physical strength yet still giving plenty of surface area for the lead.

The voltage of the battery can be used to indicate the amount of charge stored, however it isn't linear, it runs from about 12.6v down to about 10.5v, if a battery shows less than 10.5v then it is in danger of being damaged, just how much damage is not possible to say, it depends on many factors, temperature & discharge rate being the main ones. The reliability of using the voltage as a charge indicator is not brilliant as temperature and other chemical and physical processes within the battery will affect the voltage. Measuring the the Specific Gravity of the electrolyte is a better indicator, but it is still dependent on temperature also a battery can be badly sulphated and yet the electrolyte is storing a lot of charge, it just can't get out of the battery (limited current) when you need it!

If you keep the amount of discharge of a battery much less than the capacity of the battery, then it will last longer, and take more recharge cycles. It depends a lot however on the physical construction, temperatures and several other factors but again those are the critical ones.

None of the Lead Acid style batteries like being left discharged for long periods of time, after a few days what is called Sulphation starts to take place, where by Lead Sulphate starts to be deposited on the plates, this is basically an insulator which starts to limit the usable surface area of the lead plates hence causing a loss of capacity. It is very difficult to change Lead Sulphate back into Sulfuric Acid and Lead (which is where it comes from) once sulphation has started then its better to replace the battery alltogether or use it for less critical purposes in the garage where it can die peacefully!

So the main rules to get the best from your batteries are;
Keep them charged at all times.
Use them for the purpose they where designed.
Don't allow the maximum charging current to exceed about 1/10 of the capacity in AmpHrs i.e 100AmpHrs - Max charging current 10 Amps, 85AmpHrs then 8.5 Amps charging current Max.
Check the electrical connections for corrosion every 6 months, clean and tighten as required.

If you want to read up about batteries then here are some useful links:
http://batteryuniversity.com/
http://en.wikipedia.org/wiki/Lead_acid_battery
http://wiki.xtronics.com/index.php/Seal ... plications
http://www.windsun.com/Batteries/Battery_FAQ.htm
http://home.cogeco.ca/~rpaisley4/xLowBattery.html

Lot of good sites there. Remeber the monitoring voltages for batteries is only after they have been rested. The voltage on load or charge will be lower or higher than the rested voltage. The battery may well recover though it would have more chance with a smart charger. Of course when it has been recharged it will display the appropriate voltage for a fully charged battery but that will give no indication of the remaining capacity, if it holds it's charge that will be a good sign.

I bought a cheap 85A/h leisure battery 4 years ago and it's been flattened far too many times to be any good for it. However, it's never been left flat and is regularly charged by my little old Lidl charger (CTEK clone). It still holds a good charge, so I suspect that leaving them flat is the real killer, Either that or Lidl chargers are fantastic

It is not a single flattening of the battery that does the harm but doing it often, one manufacturer suggests that with using 20% of the capacity will give you 800 cycles, 50% will give you 600 cycles and 80% will give you 200. So yes the batteries life will be shorter but with care hardly noticable but make a habit of it and you nbattery will need replacing a lot earlier

francophile1947 wrote:I bought a cheap 85A/h leisure battery 4 years ago and it's been flattened far too many times to be any good for it. However, it's never been left flat and is regularly charged by my little old Lidl charger (CTEK clone). It still holds a good charge, so I suspect that leaving them flat is the real killer, Either that or Lidl chargers are fantastic

Makes good sense, that does. And Geoff, as ever, makes good sense

It was leaving my LB heavily discharged that did for it I think

All more or less true... but once as long as the plates have not buckled by having a huge jump start or battery charge with an unsuitable charger and they have just sulphated up, then they can be recovered to a large part of their original state by using a pulse charger or de-sulphation charger.

Paul