Charging batteries from the outboard

[Yammie70]

Hi,

I have 2 batteries connected to a dual battery switch. The switch is easily accessible but the batteries are under the centre console and are a pain to access...

I've looked around under the cowling and located 2 connectors with 12.2V at rest and 12.4V with the engine running (see picture).
I was thinking of connecting the clamps of my battery charger directly on these to recharge the batteries, one at a time, using the switch to select the battery.

- Is it OK to charge the battery this way ?

- Is that normal that the voltage difference between engine running and not is so low ?

Thanks!

[99yam40]

I would think the big red one would get the one start battery, but have to see how the other battery is connected to see if it is the house battery that runs everything else but the start battery.
most people use a battery tender that hooks directly to the batteries.
I would also think the batteries should read 12.7 v or above

[fairdeal]

- Is it OK to charge the battery this way ?

- Is that normal that the voltage difference between engine running and not is so low ?

As 99yam40 said, one of those large red cables goes directly to the battery switch -
so connecting your charger there is fine.

More importantly, as he also states,
your voltage values are puzzling / troubling.

With the engine running, the voltage should be well above 12.4
if accurate,
that shows the engine is not making electricity, as it should be -
but rather consuming battery power.

Perhaps that is why you are looking to charge the batteries...

[Yammie70]

hmmm, my voltmeter is not extremely accurate ($10 piece with dodgy connectors ) so it might explain the low voltage...
I will double check to make sure the batteries are charging when the motor is running.

I've never had any trouble with the batteries, I just wanted to keep them full.

[DennisG01]

In theory, you can charge the battery from any wire that eventually leads to the battery. However, generally, it's best to get as close as possible. What about screwing on a couple light gauge wires (lamp cord size, for reference... but use marine/tinned) to the batteries and bring the wires out to an accessible area? You could also do this with the battery switch - and then pick-up a ground somewhere. You'd want to properly secure/cover the wire ends when not being used to avoid shorting, of course. You could also use quick-disconnects, too - putting the same connector on your charger. Lot's of options.

Check your voltage directly at the batteries to make sure they are being charged.

[fairdeal]

However, generally, it's best to get as close as possible. What about screwing on a couple light gauge wires (lamp cord size, for reference...

"generally" it's best to have an understanding of what one is advising others about.

'lamp cord' is 18 AWG.

Here is the voltage drop calculation
assuming only a 2 foot wire length for positive and negative
and a charger output of 5 amps:



And the voltage drop calculation for the same 5 amps
with typical medium horsepower Yamaha battery cables -
2AWG, 9 foot length for positive and negative:

[DennisG01]

"generally" it's best to have an understanding of what one is advising others about.

'lamp cord' is 18 AWG.

No doubt. Also depends on the charger, though. I would hope that someone using a charger has at least a basic, working knowledge of load vs wire gauge size - or at least follows the charger manufacturer's recommendation.

However... I wasn't very clear in my response. In my head, I was responding with a charger like a Battery Minder ('bout 1.5a tops) in my head. But without mentioning that key part, it may have been confusing!