brulaz wrote:
SoundGuy: AFAIK a pair of Marine G27s or G31s in parallel should have less V drop than a pair of GC2s under high loads. Their design specs include motor starting, so I guess they have more surface area or whatever that deals with that issue. But they usually have less Ah and can't do as many cycles as GC2s.
My understanding is that 12 volt "deep cycle" batteries typically have less internal resistance than similarly rated 6 volt batteries and that's the reason they suffer less voltage drop under heavy load. It seems to me this
would be directly related to plate surface and thickness but in examining specs for various battery combinations I found AH rating isn't necessarily always in favour of GC-2s. For example, because "I know a guy" I can get a deal on
RV Care Batteries distributed here in Canada by East Penn but which in reality are Deka batteries manufactured in Pennsylvania. The G31 flooded is 20hr rated @ 105 AH, or ~ 210 for a pair, compared to 215 - 230 AH for a pair of flooded 6 volts in series. However, the reverse is true when looking at their AGM offerings - 105 AH (~210 AH for a pair of G31s) vs just 190 AH for a set of 6 volt AGMs in series.
It's become my view that a pair of 6 volt GC-2s aren't necessarily always a better choice than a pair of similarly rated 12 volt G31s, a recommendation all too often presented here on the forums. :R For those who
always dry camp and for whom maximizing battery life despite repeated deep discharge is important, sure ... but I suspect many more of us than not are only dreamers when it comes to dry camping and in fact very often only camp without shore power because we either can't get an electric site or because power to the electric site we did get has failed for one reason or another. For me that typically means I might find myself without shore power 3, 4, 5 times a season, so if I do the math there's no way that battery cycle life will
ever be an issue ... the darned battery will die of old age long before it ever comes close to exceeding it's maximum number of rated cycles. :R
Secondly, although a few here are acutely aware that no battery is going to offer maximum capability if it's not treated to a proper recharge regimen the reality is that the vast majority of RV owners have no idea whether that converter / charger is handling the task correctly or not ... they simply plug their rig into shore power the next chance they get, or a genset, and just let happen whatever will happen, regardless of whether it's good or bad for the battery, and as a result my bet is FAR more batteries than not never come anywhere near close to their maximum rated life expectancy anyway. :(
Third, as prices of decent quality pure sine wave inverters continue to drop and more & more RV owners become increasingly aware of the advantages of having one in their rig for those times they may not have campsite power, it seems to me that a pair of 12 volt G31s, because they do typically suffer less voltage drop under heavy inverter load, would in fact be the better choice for many than a pair of 6 volt GC-2s, a view which unfortunately is often overlooked by the populist clamour over 6 volt GC-2s.
JMO, but I suspect many more than would care to admit would in fact be
better served with a pair of 12 volt G31s than a pair of 6 volt GC-2s, for the reasons detailed. After all, why invest in maximum cycle life offered by GC-2s if you're only cycling a a few times each season while at the same time suffer excessive voltage drop under heavy load when using an inverter? Doesn't make a lot of sense to me. :R
