Batteries - IP 485

First, I'm surprised to not see a Yacht System category of Electrical/Batteries or something along that line.

I recently purchased a 2007 IP 485 and it's about 700 miles away currently in LA.  I knew when I bought the boat that the batteries (Lifeline GPL-27 T) were minimal, but the survey came back and reported 12.6V for the bank, but the surveyor admitted he wasn't able to check all the batteries individually. 
He recommended having each battery "load tested".

Yesterday, my boat caretaker (who knows nothing about boats) reported when asked that the 12V voltage was reporting 12.2V.  Which is too low. 
The boat has been in a marina for the last three weeks and tied to 50A power, with just the AC/Dehumidifiers and Waterpump on (on the recommendation of the previous owners). 
So there shouldn't be anything really drawing down the batteries which makes me suspect that 1 or more of the batteries has failed or they may have all reached the end of life.

I was hoping to replace the batteries this summer after we brought the boat to Puget Sound.  But with an 1100 mile trip ahead of us, I would like to have a more reliable battery bank.

So my thoughts would be to a) test all the batteries, by pulling them out, disconnecting them, and testing, 2) identify any that are really bad, 3) replace with like batteries. 
If this is a good course of action, what should I use to test the batteries?  I've always used a multimeter but the surveyor had some specialized battery tester that I didn't recognize.

How does one "load test" a battery?

Is there another course of action I've not considered?  Replacing all the batteries is ~$2500 (my guess for cost, not labor), so finding someone to replace them would also be an option. But not my first choice

Is there something else I've not considered?  If you ask me about the battery charger, at this point I will plead ignorance as I'm still learning all the boat systems.

Thanks,

Sean

Batteries are pretty important. One thing to be aware of is that it is not a good idea to mix different types/brands/styles or ages of batteries. In other words, you should not replace one battery in a pack.
If your boat is plugged into shore power, and it is on, then your batteries should not be discharged. If the charger is on. There is a huge discussion on what kind of batteries to replace with and reasons for each. The options include:
1. Golf cart batteries (flooded lead acid batteries)
2. AGM (What you have) no maintenance
3. LiFePO4 (Lithium)
Advantages to the Golf Cart batteries is lower initial cost, disadvantage is more maintenance and shorter life.

Advantage to the AGM is no maintenance and longer life than the golf cart batteries. disadvantage is that it is still a lead acid battery

Disadvantage to all lead acid batteries is when charging they bulk charge up to a point (80--90%) then drop down to an absorption charge. Meaning that it may take 1 to 2 hours to get to 85%, then 3 or 4 hours to get to 100%
Advantage to the Lithium is that you get to use more of the rated amp hours of the battery without damage. Lead acid batteries can only be discharged about 50% without damage, Lithium can be safely discharged to 80% (some will say to 100%). If you have 600 ah of AGM batteries, that means you really have 300 ah available, if you replace with Lithium you would only need 400 ah, or 4 batteries to have the same available capacity. Or, if you replaced all 6 batteries with Lithium you would have 480 ah which would be a significant upgrade.
Another advantage is that Lithium batteries are significantly lighter than the lead acid batteries (35 lbs vs 88 lbs each)
Disadvantage to the Lithium is new technology, and higher initial cost.
They are not just "drop in" replacements, all charging sources must be looked at and evaluated for compatibility with Lithium. Solar, wind, battery charger, alternator voltage regulator etc. In my case, my solar (Outback) was able to be adjusted, my alternator voltage regulator (Balmar) was also able to be adjusted, my battery charger needed a $500 firmware update, so I got a new charger/inverter.
My experience with moving to Lithium, has been excellent. We went from 750 ah of Lifeline AGM to 600 ah of Battleborn Lithium. The charge is much faster. I have seen my batteries charging at 80 amps while at 95% charged. As opposed to our old batteries that would have been at 5-10 amps at 95%

Regarding load testing your batteries. You don't say specifically where the boat is located, but there is probably a marine electrician in the area who can help you out.

Specifically, when you bought your boat you had a survey done, did you have a separate survey done on the rigging, or the engine? I had a separate survey done on the rigging, as the survey company said they did not want to check the rigging as part of their survey. They also told me that the batteries were "ok", but suggested having a load test done. The electrician I contacted did what he called a load test, but there was no load on the batteries. He came out and disconnected all the batteries and measured all voltages. End result I was told the batteries were "good at about 75-80 or capacity). They lasted until two more years, and when we had the boat in storage for the summer, they discharged to 2.5 volts. Which is when we did the upgrade to Lithium.
All batteries have a life span, typical for AGM is probably 6-8 years. Some people get a bit more out of them. Ours were a bit more than 6 years old. The batteries in my car (in the mid-west) was also an AGM, and it it made it 6 years. The AGM in my trailer about 4 years.