Lead acid batteries have several problems that lead to shortened lifespan.
Every discharge cycle shortens its life and reduces it's Ah rating, the deeper the discharge the greater the damage, this is particularly bad when you discharge below 50% of it's capacity. This effect is worsened by the fact that the last 10% (approx) of the batterie's charge has to be trickled in slowly over a long period of time and hence you're often starting a cycle from less than 100% and often 85-90% of theoretical maximum
battery capacity, so basically if you're going to avoid discharging deeper than 50% of it's capacity and your starting from 85% charge then your 100Ah
battery is only going to deliver 35Ah and this is when it's brand new! Leaving the
battery in a partial state of charge (PSOC) results in internal sulphating which again reduces capacity further. It follows that as the
battery gets partially 'worn out' a sudden avalanche of deeper discharges and lower capacity quickly destroys the
battery.
Lead carbon batteries have several advantages over lead acid.
They charge easier meaning you'll probably start each cycle from a higher charge level.
They are able to deliver many more discharge cycles over their lifespan.
They are far more PSOC tolerant and can be left partially discharged for long periods without the negative effects.
At the moment I'd probably plump for this:
https://www.alpha-batteries.co.uk/12v-100ah-ritar-agm-lead-carbon-ultra-deep-cycle-battery-dc12-100c
At £170 delvered it's only £15 more expensive than the Yuasa L36 from Halfords and I'd expect it to be considerably superior.