Battery recommendation for potential thruster

[hcooperrn]

My house battery has given up on me already for some reason, won't hold a charge for more than a day now.

I know I'm probably going to add a stern thruster in the near future; just haven't decided which solution to go with yet.

So the question is -- which batter should I go with? Is there a replacement group 24 that will do the job? Or should I try and squeeze something bigger in there to lighten the load on the alternator? Hoping to avoid upgrading the alternator if I can.

Thanks in advance!

[chpthril]

IMO, I would run the thruster on its own bank or double the capacity of the existing house bank. With that said, a larger battery capacity never lightens the load on the alternator. However, how often and for how long, would you really be using the high-draw thruster. IMO, not much. So with engine running, and a quality on-board charger for after use, the house bank should have some time to recover. This is where the extra Ah plays in. Voltage wise, the larger house bank will not be drawn down low due to the thruster and other normal house loads.

As to the existing battery that wont hold a charge. Is it actually reaching a full charge? Are there parasitic draws? Is it receiving contribution from the alternator with engine running? Id want to make sure why the battery is toast, before moving forward with any additional loads added. An issue outside of a bad battery, will be compounded with a new thruster.

[hcooperrn]

Got it, I thought maybe having more Ah in reserve wouldn't pull so hard on the alternator, makes sense that it has to replace whatever is drawn, capacity doesn't matter.

The house battery was dead the last two trips out -- I had the main switch off for sure. I pulled the batter and put it on a float charger for a few days, it reached 12.2v. After leaving it off the charger for a day though, 10v and hardly any amps.

When I get a new battery, how would I go about testing for parasitic draws with the main switch off?

[SONIC]

Disconnect a battery lead and put a multimeter in current reading mode in between the battery and the disconnected wire.
So Red lead touch to the battery post and black lead touch to the disconnected battery wire.
If there is any current flowing you have a draw.

[freeheel4life]

Got it, I thought maybe having more Ah in reserve wouldn't pull so hard on the alternator, makes sense that it has to replace whatever is drawn, capacity doesn't matter.

The house battery was dead the last two trips out -- I had the main switch off for sure. I pulled the batter and put it on a float charger for a few days, it reached 12.2v. After leaving it off the charger for a day though, 10v and hardly any amps.

When I get a new battery, how would I go about testing for parasitic draws with the main switch off?

I cant remember your year and model, but there are some years that the house battery was never wired thru the master switch.....just a thought as its something I've seen multiple times.

[hcooperrn]

Just realized signatures aren't showing, admitting I'm not the most active because the boat has been perfect so far.

'17 Z3, pretty sure it is through the master switch though, since it shuts everything off except the bilge.

Thanks Sonic, that makes sense.

[chpthril]

Ok, 12.2 is no where near a full charge. So this could mean a bad battery or a battery charger thats not up to par. Ypu can measure a draw with or without a new battery.

[hcooperrn]

My charger gets my other deep cells up to at least 12.6 usually, so I'm pretty sure this battery is just toast; my other batteries work just fine in their uses.

[Bamer]

Disconnect a battery lead and put a multimeter in current reading mode in between the battery and the disconnected wire.
So Red lead touch to the battery post and black lead touch to the disconnected battery wire.
If there is any current flowing you have a draw.

Be very very careful when your meter is setup for current measurements that you don’t place the meter leads on the positive and negative posts of the battery at the same time. You will damage your meter or at the very least blow the fuse inside your meter and get some fun sparks !!!!!!!

Other words, do the current measurement and then reconfigure the meter back to voltage/ohm measurements so you don’t forget.


Sent from my iPhone using Tapatalk

[hcooperrn]

Got it, thanks all.

[hcooperrn]

Follow-up here and one more question. I can't find any parasitic draw without the battery in with just the meter, so pretty convinced it's a bad battery.

So while replacing, and knowing I'm getting a thruster, still debating a second battery so they are the same age, now would be the time.

Can I do this as simply as adding the second battery, connecting it straight to the new house battery with 1/0 -- the thruster would connect directly to the 2nd, the normal connections including the on-board charger would connect to the normal house battery. This should let everything 'see' it as one large house battery, right?

Any risks with this or should I also isolate the second house/thruster battery?