Why Are People So Down On Gel Batteries?

[demonboy]

The key word is 'optimum', Colin. Anyone can charge a battery with anything, but there is an argument that to get the best performance from an AGM you need to be putting in a high current.

http://forums.catalina.sailboatowner...d.php?t=124973 explains it far better than I do.

[Conachair]

300 amps to charge batteries?? I think not my little demon friend!! Not unless you are towing a barge with your 3000 AH battery bank in it!

I did have to look this one up, being ever curious..

http://www.windsun.com/Batteries/Bat...at%20Batteries

And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits.

C/10 doesn't apply to agm. It seems.

[oze]

If you are going to charge or trickle charge a 12V gel battery, it requires no more than 13.8 volts at full charge, and 13.2 volts at “maintenance/trickle” charge. Make sure that your charger either analyses, or can be set on, the lower voltage. Standard charging at 14.8 volts (or more) will cause the gel to dry and reduce life and cranking capacity. Charging at no more than 2 amps is also suggested.

[Troubadour]

- For AGMs to be effective they need to be charged hard. Most liveaboard boats do not produce the optimum 300 or so amps required to charge them correctly.

I don't go with that.
An advantage of AGMs is that they will take high charge rates but it's not essential. Those sort of charge rates will only occur if you have taken the state of charge lower than you should anyway.
Having said that you don't want to charge too slowly, I would suggest having at least 20% (i.e. 20A per 100Ah) available.
Anyway that's incidental. FWIW I would have made the same choice as you have. I wondered if you'd got off the fence yet!

[demonboy]

Yes, I'm off the fence and sitting firmly in one camp now, Troubadour! Still waiting for the delivery of said batteries, mind, so I'm not a 6 volter just yet but the important step forward is me changing my mind about wets.

[Embla]

Can anyone comment on the suitability of wet cell lead acid batteries when they are located underneath sleeping accommodation? I don't have any issue with maintenance regime, but what about danger from gas emissions? My last set of AGM's (4 * 100amp hr) lasted only 2 years, so assuming there is no health issues, I will revert to wet cell type. Also need to replace bow thruster / windlass battery bank (currently 5 yr old Optima RedTop) but I wonder if wet cell batteries will cope with the pounding as they are situated in the bow.

[Richard10002]

Can anyone comment on the suitability of wet cell lead acid batteries when they are located underneath sleeping accommodation? I don't have any issue with maintenance regime, but what about danger from gas emissions? My last set of AGM's (4 * 100amp hr) lasted only 2 years, so assuming there is no health issues, I will revert to wet cell type. Also need to replace bow thruster / windlass battery bank (currently 5 yr old Optima RedTop) but I wonder if wet cell batteries will cope with the pounding as they are situated in the bow.

I lived with 3 under the bed on a Moody 44 for the best part of 3 years without issue, and one in the bow for the bow thruster.

Having said that, my alternator only charged at 13.6v, so gassing was probably an impossibility, so perhaps my experience wasn't valid.

[michael_w]

I've got three flooded batteries under my berth. Only caused a problem when the old shore power charger went berserk and boiled everything dry.

[sailinglegend420]

.......Also need to replace bow thruster / windlass battery bank (currently 5 yr old Optima RedTop) but I wonder if wet cell batteries will cope with the pounding as they are situated in the bow.

Batteries can be either starter or deep cycle that can deliver high cold cranking amps, but they must be chosen carefully. Starter batteries are designed to deliver high current for a few seconds, maybe only using 2-3 Ah, but bowthrusters may need high current for a minute or more. If 50 Ah are taken out then very large starter batteries will be needed to avoid a high depth of discharge which will kill a starter battery. This is a heavy load up in the bows, so a much better option would be much smaller and much lighter AGM batteries. Another point to consider is that starter batteries gas and must be vented to the outside – AGMs are safe anywhere.

Not all AGMs are the same - check they are made for deep cycle use.

[Mistroma]

I've just replaced my batteries and purchased 4 Trojan T105s and one Optima Red top 4.2.

Everyone will have different usage patterns and life requirements vs. cost. All I can say is that I'm happy to maintain batteries and the cost was acceptable. I downloaded a spreadsheet that allows comparison of battery types. After entering my own power usage data it appeared to support purchase of AGMs. However, when I updated the actual UK purchase costs for AGM & T105s the picture changed completely.

So I decided to stick with flooded lead acid deep cycle batteries on a cost basis despite other disadvantages. However, I was worried about the lack of ventilation in the battery compartment. The original batteries were in an unvented locker underneath the berth in the aft cabin. I haven't had any problems but was surprised that the builder didn't think it was dangerous. I suspect that the charging regime is conservative but still noticed discolouration of the locker lid.

I'm currently installing a brushless vent fan with ducting to the stern.

So my opinion is that flooded batteries underneath a berth will work. However, if you want to charge more rapidly a ventilation system rapidly becomes a neccessity to keep Hydrogen concentration well below 4%. I'm aiming for <0.5% at point when gassing will be greatest.