Starter battery capacity while fishing

My starter battery seems to have run down the other day after 5.5 hrs on the electric. Graph dimmed when starting the big motor and it turned over slowly. I had 3 graphs running and a live well running on automatic timer (although we ran it steady 30 minutes to revive a fish to release it). Its a 27 group Exide that is on its 2nd year. It tests fine under a load test. A 27 group Interstate never seemed to have ran down in similar operations after 5 years on my previous boat. Is the Interstate a significantly better battery?? I’d trade out the battery if I thought it would matter. I put a lithium jump battery in the boat just in case. I’d like to think I could fish all this all day but maybe I’m unrealistic??

captddh wrote:

Is the Interstate a significantly better battery??

Not necessarily. It all depends on how much you discharge it each use and how soon it’s recharged after discharge.

I’d bring it to a battery store to get tested. It might be worth doing your homework on the amp draws of all your devices too. You may need a bigger battery. If you bring this info to a battery store they should be able to tell you exactly the battery you need so that it’ll last a long time.

Compare reserve capacity. That will make a word of difference if one has more reserve.

I set the voltage alarm on my Humminbird to 11.5 volts.
This is what was recommended by Mercury for my 90 hp 4 stroke.
When it hits the alarm
I start the motor to recharge the battery.

3 graphs plus livewell for 5.5 hours seems like you’re asking a lot from a single group 27 battery. Do you monitor your battery voltage on your graphs? I’d either upgrade the battery to a group 29 or 31 or add a separate battery just for accessories. The peace of mind would be worth a lot.

Home Depot has exide 31 for 109$ at certain locations

A typical group 27 battery has between 85 to 100 amp hour capacity. That is completely charged to dead. You never want to discharge a lead acid battery below half its capacity. So you have about 45 amp hours available. Most devices use a little less than 1/2 the recommended fuse size to operate. So, fuse size for graphs (3 amp), fuse size for pump (5 amp). Total fuse size for your boat is 14 amps, total typical current draw 7 amps assuming the pump is running all the time. Now the math is easy. 7 x 5.5 = 38.5 amp hours used.

My rough numbers show that you could of been out another hour and a half. Your live well is a killer. Hope this give you some insight.

djshannon wrote:

A typical group 27 battery has between 85 to 100 amp hour capacity. That is completely charged to dead. You never want to discharge a lead acid battery below half its capacity. So you have about 45 amp hours available. Most devices use a little less than 1/2 the recommended fuse size to operate. So, fuse size for graphs (3 amp), fuse size for pump (5 amp). Total fuse size for your boat is 14 amps, total typical current draw 7 amps assuming the pump is running all the time. Now the math is easy. 7 x 5.5 = 38.5 amp hours used.

My rough numbers show that you could of been out another hour and a half. Your live well is a killer. Hope this give you some insight.

Maybe he had the radio on too? Plus the discharge from starting without a full recharge.

I’m guessing he needs a bigger battery.

Thanks to all for the info/advice,…especially the math from djshannon. Looks like 5-6 hours is safe. I’ll see if a lowrance hds 10 can do an alarm. Great idea.

captddh wrote:

A 27 group Interstate never seemed to have ran down in similar operations after 5 years on my previous boat.

Is this a new to you boat? Meaning the battery is different but is the load the same or different than your old boat? Could be the batteries are comparable but the demand is higher.

x2 on the other suggestions above.

I just went through this with my boat and here is what I found for me. All amps listed are typical draw that I measured or found in the user manuals.

Garmin 7610 – 1.95 Amps
Garmin 942 – 1.4 Amps
Garmin Panoptix PS 30 – 0.83 Amps
Garmin Panoptix PS22 – 0.68 Amps
Garmin Network Port – 0.23 Amps
Bilge Pump – 1.5 Amps
Back Livewell Pump – 1.5 Amps
Front Livewell Pump – 1.5 Amps
Marine Radio – 0.3 Amps (on standby) 5.5 Amps (transmitting)
Interior Lights (from boat mfgr plus additional installed by me) – 0.85 Amps
Running Lights – 0.25 Amps
Stereo – 2.0 Amps

My typical fishing amps draw is 8.9 amps. With everything running I’m at 13.0 amps. However, if everything was under max load I’m at 18.3 Amps, however I don’t see how this would ever happen in real life.

I added a second battery in the back of the boat. One battery for motor, pumps, radio, and lights. Second battery runs all the graphs, network, and transducers. So far it has worked well but I have not been on week long trip to really test the limits.

Hope this helps.

The other thing to consider guys is not necessarily about how much draw you have, but all the connections that are made. Most connections are crimp on style and they offer higher resistance then if they were soldered. The more of these crimp on connections you have and the more accessories you have piggybacking on the same connection it draws down even more.
I was having a low voltage issue when running 2 HDS units at my console. I displayed the voltage on both of them and when they were both running it was saying like 10.3 volts. I don’t put a ton of confidence in what that number says because an HDS unit will not function below like 11 at all so I know it wasn’t really 10.3 volts. Anyways I looked at my wiring for the master power switches where the HDS unit power cords were hooked up and to save time I had spliced the 2 positives together and 2 negatives together on 1 connector and attached them to the buss bar initially.
So, I basically clipped off those connectors and have them now individually attached to their own terminal on the buss bar and the voltage reading on the HDS units went to 11.4 instantly with no other changes.

So, long winded story, there could be other things going on than just your battery. Make sure all connections are tight as well.

Thanks JMP1890. You’ve got more things running than i do but it looks like 7-9 amps per hour is a good estimate with 5-6 hrs of use. I’m a skeeter guy. I wouldn’t think there would be a big difference between a MX 2025 and a MX 2190 but I suppose a 300 4 stroke is harder to turn over than a 200 2 stroke.

I’m going to keep my lithium auto start battery charged and handy rather than add a 5th battery in case I go too long.These replies have really been useful. Thanks guys.

After 7 hours of running two finders and baitwell and livewell pumps. I draw down to high tens for battery volts. I recently could not start my main motor. Luckily I have a kicker with a rope start and an alternator. I can’t speak for all kickers, but this one does not need a battery to start. 15 minutes and my main motor was able to start. Interstate size 27 800cca 1000cca on its second year; soon to be at a recycling center near you!!!

I ran 10 gauge wire direct to the battery from my HDS 12’s with a on/off switch and jumped to the voltage from 11.5 to 12.5. It also cleared up all interference.

Somewhat related. Jumper cables on board is a lot easier than swapping in one of your trolling batts to get your outboard running when main batt dies.

suzuki wrote:

Somewhat related. Jumper cables on board is a lot easier than swapping in one of your trolling batts to get your outboard running when main batt dies.