Battery trouble

"twin v8 volvo penta inboard e

"twin v8 volvo penta inboard engines (approx 25 yrs old) 1 - starter battery (new) 1 - house deep cycle (6 yrs old).
When plugged into shore power, through onboard charger, both engines will start no problem. If engines are shut off and shore power is unplugged even for a short time, as little as 10 minutes, port engine will start but starboard will only start once port engine is running and idle rpm is increased. Starboard engine will not start on it's own..makes noise like starter is malfunctioning. Further, if engines are shutoff for a longer time, 30 minutes or more, all battery voltage is lost, batteries are dead, neither engine will start without a boost. While engines are running all systems are normal including electronics. Help??"

"first off, you should have de

"first off, you should have dedicated starting batteries for each engine. Typically, there's a 'bridging scheme' (sealed relay, switch, etc) to provide emergency starting if one looses charge.

what size is the starting battery, what size are the battery cables, about how long are they, and does the battery pass a load test?

With the age of the equipment, I'd bet you have one or more bad connections or bad starter cables. You need to check to make sure each connection is clean and tight. If you find more than one, it would probably be best to replace the whole cable set. You also need a good ground cable between both engine blocks.

it would also be prudent to check the alternator wiring, too. This will ensure your battery gets charged. Check its output voltage at the back and compare it to the voltage at the battery. Anything more than a 0.2V DC drop indicates excessive loss in the wiring. (some will say 0.5V.)

This is one area where tinned, marine grade wire is worth its weight in gold.

Does the voltage really go to zero after 30 minutes of sitting?"

"Thanks so much for the info..

"Thanks so much for the info...yes, all voltage is lost as descibed and all has been functioning fine and reliably up till now?? Help the helpless... if the alternator is malfunctioning this will be a problem for the starter battery even after one start?"

yes.

where are you measurin

yes.

where are you measuring the battery voltage when it goes to zero after sitting?

is the starting battery electrically closest to the port engine?

"at the battery terminals.. ye

"at the battery terminals.. yes, port is possibly marginally closer.."

do alternators die slowly? ...

do alternators die slowly? ... if i think back there may have been small signs.. what might be the symptoms?

"Can you load test battery?

"Can you load test battery?

My limited experience indicates alternators work or don't. Apparent symptoms may show degradation but the alternator itself works or doesn't. typical, hard to start...failure to start...many different versions.

Can you start the engine and measure alternator output voltage (between its stud and the case) and then measure the voltage across the battery?

Also, see if there is a dedicated ground lead at the alternator, from its case to the engine block."

"thanks again for your help on

"thanks again for your help on this..your thoughts inspired a phonecall to my mechanic who has just called back.. seems although we did replace the starter battery..the house, deep cycle, was failing as well, resulting in, as they are in parallel, the house battery drawing power from the smaller starter battery and the recharging system could not keep up. The alternator and charging system has been tested now and once the house battery is replaced we should be up and running again..."

"All the advice is good - chec

"All the advice is good - check and recheck all connections, test alternator output vs. battery output, etc. However, you could also have a dead short in the old battery which is draining the new battery. Change it out - after 6 years it's likely on it's last legs anyway. I change my batteries every three years regardless of how well they are operating."

"You need to "de-parallel&

"You need to "de-parallel' your starting battery and your 'house battery'. Hopefully, it is as simple as throwing an existing switch."

"Some rigs have battery isolat

"Some rigs have battery isolating switches installed. I could not read or understand here [as I'm frozen... 0' cel @ 10:30...] if you have such installed. Also, some "new" batteries, even the good brands, are prone to premature failure. Do the tests as described and we'll roll on from there."