A Cautionary Tale About Batteries

[Charles]

Having had a lovely couple of weeks in Holland and a pretty trouble-free return trip across the North Sea, I was astonished to find when I went back to the boat a week later that both the batteries were completely flat: 0.64 volts in each. I knew that I had turned off all the master switches, because I always use a check list when leaving the boat and they were indeed off, so how it had happened was a mystery. Eventually, after a useful discussion with my Royal Navy son-in-law, I decided that the problem was that the float switch for the bilge pump, which is not routed through any master switch, had failed, thus leaving the pump running permanently. And why it had drained both the auxiliaries battery, to which the bilge pump is connected, and the engine start battery was probably because I have them linked in parallel so that my 14 watt solar panel keeps both topped up.
I talked on the phone to an electrician I have previously used on the boat who was puzzled about possible causes but adamant that batteries discharge that low could not be recharged. I therefore bought a replacement leisure/auxiliaries battery for about £100 and would have done the same for the engine start battery only I couldn't immediately find one. I took the discharged engine start battery home with me and put it on trickle charge for a couple of days; the voltage went up to about 12.76 and stayed there, so I took it back to the boat today and it started the engine with no trouble at all. I have replaced the float switch in the bilge - horrible job!
So:

Advice please!
Charles

[Brian & Glenda]

Some of the best written info I've ever found about batteries, I found at the Trojan Battery website. They have many useful publications and guides to aid in selecting and maintaining batteries. While I'd try to charge them, and check the holding capacity before replacing them, Trojan suggests never discharging below 80% to avoid damaging a flooded cell battery, so perhaps damage could have been done by fully discharging the battery. Here is a link to their website: www.trojanbattery.com/literature/ (I use a small portable Battery Load Tester to test my batteries on occasion. About $50 Cdn - or 30 pounds - Much easier than hauling them to the shop for testing!)

For the third question, I put a switched line between my batteries, so if my start battery was ever dead, I could start the engine using the house batteries. With the switch off, the start battery will never be drained as my bilge pump is connected to the house batteries only. (With this switch on; if the house battery was dead, I could also use the engine start battery to run the house loads, but that might leave the engine unable to be started.) This switch is a single pole single throw rotary switch, that looks just like the house and engine switches that LM installed, except it is red instead of black.

For the last question, you may wish to consider an automatic charge control relay or ACR such as: www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A
I have one connected to inputs from both my solar panel and my alternator, so whichever charging source is working at the time first tops off the main battery, then the secondary. I have my house batteries set to be my main battery, and the engine start as my secondary; as the majority of the work is done by the house batteries and the engine battery doesn't do anything except start the engine.

Hope that helps, drop a note if you want a more detailed explanation.
Brian

[Deleted]

There is no reason to solarcharge the motorbattery as its always full loaded.

[oceandancer]

Hi Charles,
I have 2 separate battery banks for house and engine both charged from a single solar panel using a dual battery solar charge controller.
These are readily available on ebay at a cost of about £20

(see www.ebay.co.uk/itm/10A-Dual-Battery-Solar-Charge-Controller-Regulator-12V-24V-for-Caravans-Boats/201835595267?hash=item2efe56c603:g:wM0AAOSwgZ1Xu1Sl.)

I also think you should invest in a bigger solar panel of al least 30w
You should disconnect the engine from the house battery.

The battery you recharged may look OK but will probably have a reduced AH capacity due to sulphation. It will probably do for now though

Regards

Mick

[Charles]

Thank you all for your advice. I will look into the solar charge controller that Mick suggests and see about disconnecting the two batteries by means of Brian's switch line.
The recharged engine start battery worked perfectly well last weekend, so I guess that I could have done the same with the auxiliaries battery too. Moral for anyone else in the same situation: try recharging first before rushing off to buy a new battery.
Charles