Battery Confusion

[jkru]

I have a pair of trojan 27SM-1100 in my 2006 searay 260. Which have never been replaced; I decided to replace them. I was back and forth, back and forth trying to find the right battery I decided on two Optima D31's over the LifeLine GPL27-T (Not sure if it was the right decision but I Optima's were about 200 buck cheaper overall).

The Problem I have is that I have this Guest Charge Pro 2622-SR model that is no where on the website. The previous batteries were lead acid. Can I charge AGMs with this charger? I would assume so but don't know. Also are these two batteries big enough for my boat? I have a 350 MPI Horizon in it and tend to run lots of electronics.

Thanks in advance!

 

[Silvertip]

Re: Battery Confusion

A group size 31 battery is larger than a group size 27 battery so you should have more power available, not less. However, group size is not the only "size" consideration. Look at the labels for Reserve minutes: xxx @ xx amps. xx Amps is usually 23 or 25. Reserve minutes is the amount of time the battery will deliver power to its loads before it can no longer deliver 23 (or 25) amps. The 23 (or 25) number is the test reference amperage and does not mean it can't deliver more than that. A battery can deliver hundreds of amps on a short term (such as starting a big engine). But the reserve minutes declines in proportion to the current draw. Example: Assume your total constant current draw is 23 amps (very high by the way for non-troller applications). Also assume the battery has a rating of 180 reserve minutes. Those two numbers mean the battery will be able to power that 23 amp load for 180 minutes before it can no longer maintain that current draw (drops below 23 amps). Now assume you have a 46 amp load (double the previous example). That then means the battery would drop out of spec at 90 minutes (1/2 the run time as you had with a 23 amp draw). It is all simple math. If you carefully compare batteries within a specific group size you will find wide variation in the Reserve Minutes and/or cold cranking amps. The bigger the numbers the more power that bucket of electricity contains.

 

[jkru]

Re: Battery Confusion

A group size 31 battery is larger than a group size 27 battery so you should have more power available, not less. However, group size is not the only "size" consideration. Look at the labels for Reserve minutes: xxx @ xx amps. xx Amps is usually 23 or 25. Reserve minutes is the amount of time the battery will deliver power to its loads before it can no longer deliver 23 (or 25) amps. The 23 (or 25) number is the test reference amperage and does not mean it can't deliver more than that. A battery can deliver hundreds of amps on a short term (such as starting a big engine). But the reserve minutes declines in proportion to the current draw. Example: Assume your total constant current draw is 23 amps (very high by the way for non-troller applications). Also assume the battery has a rating of 180 reserve minutes. Those two numbers mean the battery will be able to power that 23 amp load for 180 minutes before it can no longer maintain that current draw (drops below 23 amps). Now assume you have a 46 amp load (double the previous example). That then means the battery would drop out of spec at 90 minutes (1/2 the run time as you had with a 23 amp draw). It is all simple math. If you carefully compare batteries within a specific group size you will find wide variation in the Reserve Minutes and/or cold cranking amps. The bigger the numbers the more power that bucket of electricity contains.

Thanks for the info:

I wanted to make sure I got this correctly; here are the specs for my battery:


D31M
PERFORMANCE
Voltage 12v
Cold Cranking Amps @ 0 F 900
Cranking Amps @ 32 F 1125
Reserve Capacity 155
Capacity (C/20 rate) 75

Is reserve capacity the same as reserve minutes? If so at what amperage?
http://www.optimabatteries.com/optima_products/bluetop/specs.php

I couldn't believe it would be 75 AMPS for 155 minutes?

I love there description.. "Reserve Capacity 155". 155 what?

 

[jkru]

Re: Battery Confusion

Thanks for the info:

I wanted to make sure I got this correctly; here are the specs for my battery:


D31M
PERFORMANCE
Voltage 12v
Cold Cranking Amps @ 0 F 900
Cranking Amps @ 32 F 1125
Reserve Capacity 155
Capacity (C/20 rate) 75

Is reserve capacity the same as reserve minutes? If so at what amperage?
http://www.optimabatteries.com/optima_products/bluetop/specs.php

I couldn't believe it would be 75 AMPS for 155 minutes?

I love there description.. "Reserve Capacity 155". 155 what?

Ok just as I posted this I found some more info:

Reserve Capacity: BCI: 155 minutes
(25 amp discharge, 80?F (26.7?C), to 10.5 volts cut-off)

So that means 155 minutes at a 25 amp draw. So 2 1/2 hours?

So out of two batteries I could get five hours. Sounds a little light but I would have to work the numbers to see..

Also any lead acid battery charger should work with AGMs? The idea that you need a specific AGM charger from all the reading I have done doesnt seem to make sense as long as its delivers the correct voltage range to your battery correct?

 

[Silvertip]

Re: Battery Confusion

Think about the money you are about to spend. I buy my deep cycle batteries at my local farm store (Fleet Farm). A group 27 with 175 reserve minutes at 23 amp draw is about 75 bucks. Why would you spend hundreds for larger batteries (physical size) with less capacity. Yes -- they may last longer but that's a big if. Even so, I can replace these inexpensive batteries every three years and still be way ahead financially. I have never had to replace one of these batteries because it failed. The batteries always went with the boat when I sold it and they were working fine.

 

[Fl_Richard]

Re: Battery Confusion

+1 on the old fashoned Lead Acid technology.

AGM's are the latest and greatest but are they really better and cheaper in the long run? I think not.

 

[bruceb58]

Re: Battery Confusion

AGM's are the latest and greatest but are they really better and cheaper in the long run? I think not.

Depends on the application. I have one in my Harley. The vibration resistance alone is worth getting it for me. Also, its nice that it doesn't self discharge as easily. So..if you have a high vibration area and you also need a battery that can be tipped without leaking and want a low self discharge, then an AGM is a good choice. Most boats probably don't need it though and i wouldn't buy one for my boat.

 

[jkru]

Re: Battery Confusion

So I have a couple thoughts. I think each poster brings up very relevant points and thank for all the education to get me off to a good start. Based on what knowledge I have gathered and have to date I view my decision this way. I have a tendency to run my batteries down for many reasons, the most common being forgetfulness. I also am on the Puget Sound with my cruiser were at times becomes choppy. Another thing is I have enough maintenance on my boat, including lay-up for the winter, without having to add maintaining flooded cells to my list. The last but not least is reliability; ok $100 per battery more reliable?? Maybe not, but my son and wife are worth every penny not to mention my piece of mind (The little I have left  ).
$200 dollars extra for ?high? end battery bank is only $2 in boat money. For me, I think it?s worth the extra piece of mind.

 

[bruceb58]

Re: Battery Confusion

Maybe its me but for batteries that may get run down further, I would go for Trojans.