Dead Batteries - Are they really dead?

[fragmeister]

Hi Raiders,

I had a battery issue last weekend and how I dealt with it may be useful information to some Raiders.

My boat batteries are about 5 years old. I have 2 deep cycle batteries for the minkota that are showing signs of age and a dual battery system for the boat itself.

I replaced the two boat batteries last week and topped up the charge before covering up the boat again.

There are a few things in the boat that draw current directly from the battery (mainly the sound system) so I have to top the charge up about once every 2 weeks.

However, there is some issue causing excessive drain that I will need to resolve but the result was when I checked the batteries two weeks later one was absolutely dead flat.

I hooked up the charger ( I have two anderson plugs conveniently loacted behind a panel in the gunnel so I can plug in the charge easily) but the charger just came up with an error message.

This is because modern chargers are designed to be "Safe" so they will not commence a charging if they are not sure that it is a battery they are connected to.

My battery was dead flat and had a terminal voltage of 5.5 Volts. So the charger is not sure that this is not a 6 volt battery and it may be unsafe to charge. Fair enough I think.

To overcome this I took a charged battery ( I have a  small 12 Volt backup battery for my shed alarm) and I connected this to my dead battery , (positive to positive and negative to negative) and then connected the battery charger. The charger commenced to charge and I left this for about 30 minutes until the dead battery had a little surface charge in it and then disconnected the good battery.

The charger continued to charge the dead battery and after 2 hours the terminal voltage of the dead battery was up to 12 volts and I was able to turn the charger off and then back on again and it  recommenced the charge process without issue.

12 hours later the battery is fully charged and at this stage I belive that it is fully recovered.

I learned this trick many years ago from a training course I did at Exide batteries when I was working as an electirican on battery opperated forkifts.

In the "old days" chargers were not as sophisticated and they just pumped in the current as long as they were connected. This was far from ideal and could result in overheating, excessive electrolyle loss, excessive gassing and  shortened the life of the battery, but you never had a problem where the charger failed to at least try and charge the battery.

I hope this helps anyone who has a dead flat bettery and a charger that fails to "see" the battery

Cheers

 

Jim
 

 

 

 

 

 

 

 

Edited November 11, 2022 by fragmeister

[xerotao]

Different batteries require different charging algorithms. “The old days” most batteries would be lead acid and thats what a dumb charger would do.

what type of battery is your new one? As i know my lifepo4 battery requires a “jumpstart” when it dips under 10v to wake up the bms. When my redarc bcdc does not see it

[noelm]

If your battery was down to 5.5V with no load applied, you have an "issue"

[fragmeister]

8 hours ago, xerotao said:

Different batteries require different charging algorithms. “The old days” most batteries would be lead acid and thats what a dumb charger would do.

what type of battery is your new one? As i know my lifepo4 battery requires a “jumpstart” when it dips under 10v to wake up the bms. When my redarc bcdc does not see it

Lead acid. My smart charger can handle many battery types but like most it can’t handle dead flat ones.

 

39 minutes ago, noelm said:

If your battery was down to 5.5V with no load applied, you have an "issue"

They can get low when they are absolutely dead flat. Like I said…I recovered the battery and I have done this before in similar circumstances. It won’t work on sulphated batteries but there is a different strategy for that. This battery was only 2 weeks old and had been flat for about a week.

 

[Rebel]

Great Info.

Thank you.

[bessell1955]

Great advice, I will keep it in mind.