You might not use a grease gun often, but it's very handy to have your own once the need arises. The voltage on this tool is 18 volts.
From B&Q
Makita Dgp180Rt 18V Lxt Cordless Grease Gun + 5.0Ah Battery + Charger Dgp180 - One Size
Buyaparcel
Makita DGP180RT 18v LXT Cordless Grease Gun + 5.0Ah Battery + Charger DGP180