Spare battery storage on bike?

[glenno]

I am wondering if anyone has come up with a way to carry a spare battery on their Ride1Up LMT'D bike? I bought one last Fall and I would like to extend my range by having a spare battery to snap in when the juice is getting low. I like the looks of the Ride1Up accessory bike carrier but I question whether it would be strong enough to carry a replacement battery, which is quite heavy. I would be concerned about losing the battery should the bottom of the pannier sack give way. I have looked at small, generic bike carryalls although the size of the battery is not easily matched.
Any suggestions (other than decreasing power assist to lengthen range) would be appreciated.

 

[rcdanner]

On my LMTD ST I use Ibera Rack and small 18L Lumintrail Bag to carry my extra battery. Battery fits kitty-corner inside the bag.Very secure. Easy to mount/dismount bag. Very low profile on the rack so it doesn't make swinging my leg over too awkward when mounting the bike. I originally used just the rack to carry the spare battery securely wrapped in a towel with bungee cords. But the added height was awkward.