Lead a is charge

PabloPicasso

PabloPicasso

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I've brought my two 12v lead acid boat batteries home to give em a charge up. They've been sat unused and unloved all winter.

The water levels look OK.

How long should I charge them on my car style mains trickle charger.

Overnight, or until the amp charge rate drops to a low level?

Anything else useful I should consider
 
Basically you should charge with amp hours of charge commensurate with the stated AH capacity of the battery. ie something like 130% of AH rating. Now I am guessing that being a trickle charger it doesn't have an amp meter but delivers around 1/3 amp. I am guessing you are taking 80 Ah batteries. Fairly heavy to lift but nopt back breaking. So if those guesses are right you need to charge for 240 hrs for each battery. I would suggest you charge both at once ie in parallel .
The concept of "trickle charge" is that charge current is so low that you can not over charge a reasonable sized battery leaving it on long term. So just leave the trickle charger on both batteries until you need to take them back to the boat. (all guesses) ol'will
 
PabloPicasso said:
I've brought my two 12v lead acid boat batteries home to give em a charge up. They've been sat unused and unloved all winter.

The water levels look OK.

How long should I charge them on my car style mains trickle charger.

Overnight, or until the amp charge rate drops to a low level?

Anything else useful I should consider
Click to expand...
It depends on:-
  • Their size ( Ah capacity)
  • Their current state of charge
  • The output current of the charger

Use an automatic charger and you can leave them ( individually )until the charger indicates that they are charged.

Otherwise leave each on charge until the volts have risen to 14.4 and been maintained at that level of a couple of hours. Stop the charging if the volts rise much above 14.4.

One of Lidl's or Aldi's little automatic 4 amp chargers for around £13 could be a good purchase. ( My Lidl one eventually drops to a 50mA output so I can safely leave a battery on charge almost indefinitely )
 
Some of the smart chargers even have features to cycle or revive batteries before - when charge is done - automatically go into maintenance mode.

While at it, I'd do a load test (individually) before fitting them again. Just to check the condition.

Btw batteries survive winter well then stored fully charged, and disconnected from anything consuming power. No issues with freezing when fully charged so can be left onboard.
 
OK. Useful replies. I'll see if I can get one of those lidl chargers

One battery is 85ah, the other 120ah. Normally charged from the alternator to the smaller start batt, then by a vsr to the larger one
 
PabloPicasso said:
OK. Useful replies. I'll see if I can get one of those lidl chargers

One battery is 85ah, the other 120ah. Normally charged from the alternator to the smaller start batt, then by a vsr to the larger one
Click to expand...
The Lidl ones are only available when they are Middle of Lidl special offers which l though they were at present , but not so.

The Aldi ones should be available online.
https://www.aldi.co.uk/auto-xs-car-battery-charger/p/813260585046300

It'll take a while to recharge a big battery especially if its like the Lidl one which reduces to 0.8 A once the battery is about 75% charged.
 
If they are traditional wet lead acid batteries, one way of checking them is to use a hydrometer. This is assuming that you can get access to the cells to extract some of the acid...
A hydrometer will tell you what's happening to the battery and when it really is charged up fully. After that a load test is the next stage in truly assessing a batteries condition. (As in monitoring the voltage over an extended period of time with an appropriate load drawing current from the battery. Not a CCA drop tester as that only tells part of the story.
I think you should get hold of something a bit beefier than a trickle charger to charge them up to 100%. You'll be there for days and days with a trickle charger...

edit. Apologies if I'm teaching you to suck eggs and this is all old hat to you.
 
Last edited:
john_morris_uk said:
If they are traditional wet lead acid batteries, one way of checking them is to use a hydrometer. This is assuming that you can get access to the cells to extract some of the acid...
A hydrometer will tell you what's happening to the battery and when it really is charged up fully. After that a load test is the next stage in truly assessing a batteries condition. (As in monitoring the voltage over an extended period of time with an appropriate load drawing current from the battery. Not a CCA drop tester as that only tells part of the story.
I think you should get hold of something a bit beefier than a trickle charger to charge them up to 100%. You'll be there for days and days with a trickle charger...

edit. Apologies if I'm teaching you to suck eggs and this is all old hat to you.
Click to expand...
Just another note of caution. I have a very old 4 amp basic transformer rectifier type charger. (A little red box with an ammeter and a pair of croc clips) If the battery is really flat it will take more than 4amps and trip the charger! I also have a more modern "Smart Charger" and sometimes that wont kick in with a very flat battery!
 
If they were half charged or more when you left them and they were in good condition, they will be fine. Your trickle charger will bring them up to full. It might take a while, though!
 
neil_s said:
If they were half charged or more when you left them and they were in good condition, they will be fine. Your trickle charger will bring them up to full. It might take a while, though!
Click to expand...
I disagree. There will be some sulphated areas of the plates. LA batteries must be store fully charged and top up charged monthly to replace the lost charge in store which is inevitable.
 
Solar panel got disconnected end of October - I went on board last week - both batteries show 12.8 volts. No other source of charging!
 
Can still be in poor condition even if showing 12.7 v . Especially if it got to this voltage in short time . Do a load test from fully charged with known load eg 40 watt bulb and check voltage every hour, will tell if battery is OK or not. A badly sulphates battery can show 12.7v and drop like a led balloon under load.
 
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