Odd Battery Question.....

[Wishiniwuzfishin]

Is hooking up (parallel) a partially charged battery to a known fully charged battery helping or hurting? I have been wracking my brain trying to figure this out and all I'm doing is making myself dizzy. I have a 1974 115HP Johnson that is sometimes stubborn when starting. If I don't do everything just right the motor sometimes will not start and it sucks the juice out of the battery pretty fast. I know that battery is in good shape and I always try to start out fully charged. I have another older battery that according to my good old hydrometer is only charging between 50 and 75%. My question is am I helping the situation by hooking up the partially charged battery parallel with the first, or hurting things by hooking it up. My own opinion is as long as the second battery is providing some amps it is helping. Anybody have some logic to show me otherwise. I'm even interested in hearing any other opinions also. Thanks in advance.

 

[BaileysBoat]

Re: Odd Battery Question.....

You can't test any battery with a hydrometer. A good hydrometer reading only indicates the battery is ready to be load tested.

Have you done a load test on the "known good battery"?

 

[Lyle29464]

Re: Odd Battery Question.....

The 50% battery would make things worse.

If they were both 50% the second battery would help a bit but not much would work. maybe a small light bulb.

The low battery would be taking some of the power that could go to the motor.

 

[Wishiniwuzfishin]

Re: Odd Battery Question.....

"You can't test any battery with a hydrometer. A good hydrometer reading only indicates the battery is ready to be load tested.

Have you done a load test on the "known good battery"? "


I really don't see how that applies to my question.
But no, I have not done a load test on the "known good battery". I KNOW it is a good battery. I have used it in other applications and it functions perfect as a battery should. I realize I may have other issues with the motor but sometimes it is hard to troubleshoot a motor if it won't start. Even if there are issues that are causing my battery to drain faster than normal, I still wonder if hooking up the other battery is helping or hurting.
Here's my logic. With no battery, obviously the motor won't crank. With a partially charged battery the motor may or may not crank but there's a better chance than no battery. So.....with my logic, using a partially charged battery is better than none at all. Where I start to wonder is what the effect is on hooking it up to another "known good battery".

 

[Laser87]

Re: Odd Battery Question.....

The battery you refer to as good may have issues. The specific gravity readings should be 1.220 to 1.260. A specific gravity reading of 1.300 is a fully charged battery.

If your battery does not last long check the sticker on the battery for the Cold Cranking Ampere rating. The battery may be too small.

A fully charged battery should have a 12.6 to 12.8 DC voltage reading. A partially discharged battery would probably have a voltage reading of 12.0 to 12.2 volts.

When you connect the two batteries in parallel there will be a current flow from the good battery to the partially discharged battery. Connect the batteries just before starting the engine and use caution when disconnecting the batteries because of the hydrogen gas that will be present.

When you crank the engine the battery voltage will drop on both batteries, and the good battery will provide most of the amperage required, the partially discharged battery will also provide current to the starter motor.

 

[Wishiniwuzfishin]

Re: Odd Battery Question.....

The battery does not have issues. It is fully charged and the CCA is more than adequate. Are you saying the battery should crank the motor over forever without any recharging?
All I am asking is:
If the "good" battery will crank the motor over for.....let's say hypothetically......3 hours before going dead......would hooking up the other battery in parallel, add to that 3 hours?

Any problem I might be having with not enough cranking time is a motor issue and not a battery issue. I'm just looking for a way to get the most cranking time possible.

 

[Lyle29464]

Re: Odd Battery Question.....

Yes the 50% battery will add to the total amps. BUT your engine will not turn as fast for the first few minutes, The 50% one will not help the engine start. It will hurt it until the 100% battery is discharded to its level. The second battery would need to be almost at the level of the first one to help your starting. Now if you were seeing how far a electric car would go all the batteries you could hook up would help. but if you wanted to race a block( like starting and engine) you would go with the 100% one only.

 

[Lyle29464]

Re: Odd Battery Question.....

If the "good" battery will crank the motor over for.....let's say hypothetically......3 hours before going dead......would hooking up the other battery in parallel, add to that 3 hours?

Yes BUT that will not help you out. The battrery with lower voltage will lower the voltage to your starter, power pack, coils and then your plugs.

 

[LippCJ7]

Re: Odd Battery Question.....

yeah hooking up your battery that has limited holding capacity will help but in my experience it will only help for a short time, I have found that batteries, once on their downhill side of life tend to fall off quickly so be careful bud!

 

[Wishiniwuzfishin]

Re: Odd Battery Question.....

I think I'm starting to see your point Lyle.

 

[Lyle29464]

Re: Odd Battery Question.....

I think I'm starting to see your point Lyle.

great I was getting ready to call in the big guns. silver etc.

I guess the ez way to figure it out would be to answer 2 questions

1. If you forget about the second battery what will the voltage be on the cable from the battery to the starter when the key is in start? (10 volts?)

2. If you hook a battery cable from a battery with 6 volts in it to a battery with 10 volts in it, what way will the current flow?

 

[Wishiniwuzfishin]

Re: Odd Battery Question.....

Ok....so here's another question..... (and I'll probably be sorry I asked ) My battery is fully charged, "load test passed", and 700 CCA. The motor ignition system, battery cables, connections, solenoid, starter etc etc etc are all functioning correctly and in great shape. There is nothing abnormal that would cause excessive battery drain other than the normal draw when starting, but my motor won't start. Maybe I'm out of gas Any guess as to how long my battery will be able to crank the motor over at speeds and voltage required to start engine? (1974 115HP Johnson) Of course, I don't mean constant cranking for 5 minutes straight. Just like one would normally do if trying to start an engine that won't start....like maybe crank 5 seconds...pause 10 seconds etc. How long will my battery have enough power? Just like to hear any guess...10 minutes.....10 hours....10 days??? Also a normal boating day temp like 80 degrees. I don't think I would be boating if it was 10 degrees.

 

[Lyle29464]

Re: Odd Battery Question.....

You need to post the starting probem in the outboard section. They will get you started in the right direction. If your engine will not start in the first "FEW" seconds something is wrong and I would not leave the dock. The little starter motors on a v4 will not take much grinding. If you pump the bulb till it is hard,( arrow pointing up) set the fast idle level up a bit and push (key) choke in and at the same time you turn the key it should start the first or second time over. thumb the choke every second till it starts to bog the engine down then idle it back down to normal. If that will not start it you have went past my paygrade

 

[Wishiniwuzfishin]

Re: Odd Battery Question.....

I've been thru all that with the starting procedure. My bulb arrow is pointed right. Has a toggle switch choke. I guess I'm just bored today and thinking up stupid questions. I was just curious as to how long the battery would crank the motor if it had too.