Replacing batteries

[Shantih]

I own a Bavaria 46 new in 2005. She has operated as an RYA RTC and charter yacht so regularly in use for around 24 - 30 weeks per annum. She made 5 voyages to the Med and back for winter sailing until 2011. The first set of lead acid batteries (3 x 145 AH) performed well for 4 years and the new set have done the same . . . until recently due to an oversight with shore power charging when they drained completely over a 2 week period. Now on charge but I fear will need to be replaced. I understand it should be possible to benefit from a much longer battery life. So what with is the question please, gel or the same or something else?