Battery boo boo, what to do

[Longbranch Louie]

I returned to our tug after 6 days to find I had forgotten to switch on the shore power after connecting to the dock. House batteries were dead as the frig had been on. Garmin, thrusters etc didn't have enough juice, and dc panel showed no charge with engine running until I paralleled the batteries. After a short time I took off parallel and dc showed charging at 14 and everything worked ok. My question concerns damage to the batteries. Ive heard your not supposed to allow house batteries to drain down. Have I damaged them and or will they recover to full use now? I don't want to have weak house batteries just before heading to Desolation sound. Is there anything else I should do to help them recover? Add water??

 

[Ainokea]

I would check the water level and top off if needed with distilled water. Depending on the age of your batteries you may be ok. I have accidentally drained the house batts and after a recharge they were fine.

Frank

 

[trailertrawlerkismet]

I'll add on to what Frank stated with this....if your Ranger Tug has a battery charger/invertor it's my understanding that if set up properly your batteries will shut down before they become damaged beyond restoration, the R27's are this way. Unless the batteries are real old you should be fine but to be certain you could have a load test performed.

 

[South lake]

I bumped the battery charger switch and turned it off accidentally last year. When I got back to the boat the fridge had drained the batteries. Charged them up and they've been fine ever since. I did put a guard over the battery charger switch as well.

 

[Levitation]

Longbranch -
I agree with everyone that you are likely OK. A single hard discharge does not usually fry the batteries if they were in reasonable condition to begin with. I would not get carried away with load testing at this time. unless you see a problem after the batteries have had a good charge.

DO top off the batteries with fresh water - I bet they need it anyway. Let me know if I am right .
(if I'm wrong, let there be dead silence :mrgreen: )

Now, the reason you did not see any charge happening on the house set via the engine/alternator right after starting up is because the starter battery was still recharging and had not yet reached the magic number (roughly 13.6v - 13.8v) to flip on your Blue Seas relays and parallel the engine battery over to the house set.
(or else the relays are not wired correctly - which has been known to occur)

In the future have a small bit of patience before flipping the parallel switch - to let the starter battery catch up - and the Blue Seas relays should do the parallel switching anyway once the starter battery is up to voltage. Give the engine 3 minutes and look at the voltage panel before flipping the switch.

The reason for this delay is a situation (not real likely - but not impossible) where your house set has discharged down (maybe too long out on the hook) and the starter battery may not be fully charged either (for what ever reason)
Now you start the engine (on the starter battery's last gasp) and run back and flip the parallel switch - and the engine stalls (for whatever reason - like maybe Murphy does not like you 😱 )
Now you have your starter battery essentially shorted out due to the discharged batteries put across it when you flipped the switch. At this point all the batteries are down to the point that the engine may not crank or may not crank fast enough to start. And also low voltage can cause your engine ECM to not allow the engine to start.

So there you are. Still on the hook. Dead engine. And no cold beer left in the warm fridge.
This is what is known as an emergency.