I used to have Optimate 3s on all my bikes, but when one died (and I couldn't figure out why!) I bought a cheap trickle charge from Aldi to replace it rather than another optimate.
The 748 now lives on this charger and I simply fitted an optimate connector on the end which I already had but you can buy for a couple of quid.
This was the charger. Although it's no longer available, they do sell them every so often so keep your eye out for them. Or just buy a generic one off ebay
https://www.aldi.co.uk/auto-xs-car-b...90030347442700