Questions about boat batteries

**Nautiquehunter** · 04-15-2018, 06:47 AM

How old are the battery's you ave now ? Why would you want to get a less powerful battery? Size is determined by the space they have to fit in. Just measure the old battery's.You need starting battery's not deep cycle.

**MLA** · 04-15-2018, 08:57 AM

1) it never hurts to upgrade battery capacity as a boat/vehicle ages.
2) moving the switch with engine running, depends on how the switch is made. Some are safe to switch others are not. No, with engine running, you will not see battery voltage but rather the alternator voltage. You would need the engine off in order to read the level of each battery. However, if you have an analog needle gauge, you likely not be able to get an accurate status. Reason being, a full battery is a round 12.8-13.0 and a dead battery can be 11.8. Hard to see the tenth of a volt on a needle gauge.
3) Voltage is best an easiest way to check a batteries state. This wont necessarily tell you the battery is a good or bad yet, just charged or discharged. You need to charge, or attempt to charge the battery to full capacity to know further.
4) the group size indicates the physical size/dimensions. A 24 is the most common and smaller of boat batteries. A 27 is larger and has more capacity (typically) and a 31 and 29 are a little larger and a little more capacity.

**wakehead** · 04-15-2018, 08:08 PM

My batteries are 4 years old. I just bought the boat and the dealer said they were a little weak. That's why I want to heck them. Thanks for the information. That is a great help. What should the meters read if I plug them onto my battery ?

**MLA** · 04-15-2018, 08:26 PM

@ 4 years old, fully charged after the surface charge wears off, anything above 12.5 is good.

**functionoverfashion** · 04-16-2018, 03:54 PM

The dealer probably put a load tester on the batteries (something like this) which more or less creates a dead short across the battery, then reads the voltage drop as a simulation of the starter's draw. The simple ones have a needle that moves along a gauge, and if it points at the "OK" area, but drops below after a few seconds, then that's probably what they're seeing. A brand new healthy battery will hang in the OK region for 10 seconds.

Everyone probably has a different idea of how long a battery should last, but 4 years in a boat isn't an unreasonable lifetime, nor is it unreasonable to replace after that period.

So, basically... if you want to test them yourself reliably, get a load tester. You could probably get away with another season, but if you sit and listen to music a lot, your batteries might not last the season.

As far as a replacement battery, look for one with the same CCA or MCA (cranking amps) rating as the one(s) you have. If you DO sit and listen to music, drawing one battery down on a regular basis, you should consider a deep cycle battery for that use - if you can separate them in that manner. I did this for years with my old Supra, and after replacing starting batteries every few years, my deep cycle lasted for 8 seasons of use.

**MLA** · 04-16-2018, 05:54 PM

with 30+ years in the car and boat biz, those toaster-testers are one of the most misused tools ive seen. 99% of the time, the user clamps on a dead battery and loads it up the says "yep, she bad". Its like X-raying a compound fracture to see if its really broke. If you load test a battery thats not fully charged, the predicted outcome is a failure.

So if a battery cant reach an acceptable full charge, no need to to even load test, its done. In most cases, if the battery can reach an acceptable charge, it will pass a load test.

**wakehead** · 04-16-2018, 08:06 PM

Thanks guys. Can I run a deep cycle and starting batter at the same time. Basically set my dial to all ? Is there an advantage to that ? Or do I need to manually go to the back and switch when I go to listen to music for example

**Infinity** · 04-16-2018, 11:49 PM

Why would you want to set your dial to "all" unless you need more CCA to start boat? If you forget, you run risk of draining your starter battery while playing music. Maybe I have different switch than you but I have starter battery and deep cycle for acc stuff and I only turn switch to 1 so my starter is the only one that is used to start and all else pulls off acc deep cycle battery. I would only combine if I was having trouble with my starting battery. I am pretty anal about trickle charging them all after weekend tho so hopefully that does not happen....I also check acid levels in Spring, actually just checked all 3 of my batteries last week, none really needed it, but I topped them off to be sure.
MLA knows the most about that stuff tho, he actually added a 3rd battery for my last summer (have 2 for acc and 1 for starting). Just more juice for stereo and I fill ballast with engine off to keep hours down tho 3 batteries are likely not needed, figured not only does it help give me a little more juice, but also good ballast!

**functionoverfashion** · 04-17-2018, 01:31 PM

Originally posted by MLA View Post

with 30+ years in the car and boat biz, those toaster-testers are one of the most misused tools ive seen. 99% of the time, the user clamps on a dead battery and loads it up the says "yep, she bad". Its like X-raying a compound fracture to see if its really broke. If you load test a battery thats not fully charged, the predicted outcome is a failure.

So if a battery cant reach an acceptable full charge, no need to to even load test, its done. In most cases, if the battery can reach an acceptable charge, it will pass a load test.

You're absolutely right about the load tester - the Toaster is what I've heard them called too. They're only useful on a fully charged battery, and that's how we always used them in the past. Good points, and the load test is just one method, if used correctly, to check on a battery's health.

**windsurfnut** · 04-27-2018, 10:27 AM

A really good bang for the buck is the Exide AGM Dual Purpose battery @ Costco. Its a high end battery, tons of power and longevity.

**wakehead** · 04-29-2018, 01:25 AM

Thanks windsurf, does anyone have any suggestions on the battery brand to buy. I have been looking at the interstate brand but curious if there is something better out there at a reasonable cost.

**MLA** · 04-29-2018, 07:14 AM

Better at a reasonable cost is going to be tough, if you are referencing off Interstate. They are a quality battery and a mid level price. There are a couple better brands, but you WILL pay more. Cheaper price, gets you a cheaper brand.

**Joshua J Rowe** · 05-01-2018, 09:03 PM

Starting batteries are not designed to be drawn down. They store much less energy, but can produce high current with minimal voltage drop for short bursts. That's what they are designed for.

Deep cycle batteries are the opposite. They are designed to discharge at a specified rate, or less, for a period of time. They have more voltage drop as current increases which is why they are not good starting batteries.

Dual purpose are decent at both. I am a big fan of AGM batteries.

Battery types, what/where/why can be an in depth discussion.

You do not want a starting battery and a deep cycle battery connected together with your music on. If you chose to have one of each you would run your music on the deep cycle, then switch over to the starting battery to start the engine. With engine started connect the deep cycle again to charge it.

If the battery running your music was drawn down to say 10 volts and your starting battery was at 14 volts, the deep cycle battery would be drawing current from the starting battery, discharging it. Furthermore, because the deep cycle battery has much higher storage capacity, it can drawn down the starting battery's voltage without recovering an equal voltage. Hard to explain without going on forever. If one is at 10 volts and one is at 14, if they were matching batteries they would balance at 12 volts. If the 10 volt battery has more capacity than the 14 volt battery the final balanced voltage will be less than 12, possibly not much above 10.

Either match them or use them for their intended purpose.

I cannot comment on what you could do with the boat running as I do not know how the system was designed. I doubt you would want to switch on one and switch off the other at the same time. Typically with a battery transfer it is best for the electronics to start with one on, connect(turn on) the other, then disconnect(turn off) the first. Your electronics do not want to have their voltage source and ground interrupted abruptly or erratically.

**Joshua J Rowe** · 05-01-2018, 09:08 PM

Northstar are great, often rebadged as they manufacture for others as well as their own brand name.

I use one of these AGMs from West Marine. I forget who manufactures them. Most of these batteries are from a short list of manufacturers.

https://www.westmarine.com/buy/west-...BoCMgoQAvD_BwE

Questions about boat batteries

Questions about boat batteries

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