xjr flat battery

[jas xjr]

i have been away on holiday/business for 17 weeks. on my return i find i have a completely flat battery. i cannot open the boot to gain access to it either.have tried the key but to no avail.
i do have a little gadget in my loft that allows one car to charge anothers battery via the cigar lighters,is this safe? or can anyone suggest anything else? thanks in advance

[jas xjr]

thanks.more at home with wd/40 than anything else,haha. will try under bonnet option if wd/40 fails. cheers!

[jas xjr]

i was ready with the jumpleads and battery but wd/40 sorted it in the end. thanks for the advice. 99xjr