I do not think you will get a Panasonic battery for £70. I paid £112.92 in September 2009. That was with OC discount and VAT was 15% at the time. On the other hand if you can buy Panasonic batteries for £70 I would buy as many as you can lay your hands on! Good profit margin!
Regards Geoff Peace.
When I got my Panasonic battery about a year ago for about £70 the dealer could only get 2 at those prices as I had the idea of get a few to sell on Ebay. 
These seem to be on offer from time to time.
Just looking into this myself, one thing for sure is that the Wesco is a complete waste of time, ours failed after a few months and we even purchased the Opti 4 at the time to trickle and keep it in tip top, so not pleased with it. Wouid not hold the charge and we had to keep topping up.
Having not used our MX5 for 2 months we attempted to trickle charge the battery, that usually works but all we got was a display of warning lights and no turnover, deadly silent. We have recently read that this would be due to a dead battery though not a surprise it is getting old.
We would not mind the panasonic but the Lion brand looks a better specification and more useful for infrequent use. Does it have vents like the panasonic battery, or should we just get the original panasonic battery?
thanks,
MX5parts has the Panasonic for £99.60 now there was 10% off a few weeks ago.
So at todays price just buy the Panasonic I got one a few weeks ago from MX5parts.
I have one of those Lion batteries
It is sealed so should not leak and correode the boot nowhere to connect the vent pipe anyway.
I have had it since Dec last year bought when Europcarprts did the same offer. There is a deport near on e of the places I work so I did click and collect.
If you can get the panasonic for £70 buy a bulk load and make some cash