25d alternator 13 v charging?

[frankfurder]

I have always, since 1996 had 14 v alternator output as measured on the panel. Lately I have noticed 13v when charging. I use a small solar panel to charge my 2 battery bank.

I assume the voltage regulator is internal to the alternator and I should check voltage at the battery and alternator output , plus clean terminals before pulling the alternator for testing.

Is it possible that one bad battery would keep the alternator from charging @14v when on both?

[Steve Laume]

At what charge are the batteries? Do you charge them together as one or do you alternate the charge between the two of them? If you are charging them independently, do you notice a difference in the voltage output?

If they are near to full charge, the alt will not put out the maximum voltage, Steve.

[frankfurder]

Steve, when motoring I charge both batteries, when in the slip the solar panel charges one at a time. With the summer sun, I may have fully charged batteries if that results in lower alternator output.

[Steve Laume]

Someone correct me if I am wrong.

It is generally not a good idea to charge both batteries together unless they have been tied together since they were new. If one battery is at a lower charge state than the other, the voltage regulator will respond to the total. This may result in over charging the full battery and not optimizing the charge on the weaker battery. You could so harm to your batteries if one is fully charged and the other is calling for all it can get.

Many people use one battery for starting and then recharge it before switching to the other to be used as the house battery. You can alternate their use by the trip or by a set time period. You are always charging one battery at a time this way. It also keeps one battery in reserve to act as a starting battery so you never find yourself in a situation where you have run down the entire bank and cannot start the engine to recharge them.

There are ways to charge both batteries at the same time. With a simple battery selector switch this would not be the case, Steve.

[frankfurder]

Today I found battery 2 discharged and batt.1 fully charged. When I removed Batt 2 from the charging, alternator put out the normal 14v. For some reason, I have replaced batt.2 every 2 years while batt 1 remains good?

Same starting battery, 1000 cca. Am thinking of going with agm mixed with batt 1 wet cell until it fails.

[Steve Laume]

Before you spend hundreds of dollars on batteries, you might want to spend ten bucks on a book that might save them from an early demise.

https://www.amazon.com/12-Volt-Bible-Bo ... 0071392335

Never mix battery types, Steve.

[RC James]

Re: 12V Bible
Just be advised than when he references "TRANSDUCERS", he means 'energy absorbing devices-- Nav/interior/exterior Lights/Motors-starter&refrig/bilge- and Electronics................ie. anything that uses 12V power.
Took me awhile to get my mind off the depthsounder thing-a-ma-bob and absorb what he meant.
RC/KittyHawk,NC 25D