If the battery wasn't swollen prior to use, that would indicate there is something in the wiring shorting, so probably worth getting the wiring/gearbox checked. LiPo's don't just randomly do that without a reason.
Li Ion's are a noob trap - they don't have output and are more not less, likely...
Possibly not the greatest idea bitching about it on the internet prior to travelling, ESTA can still be revoked and they can potentially request 5 years of social media history prior to entry, as the 60 day consultation expired on 9th January.
The place it should be is https://airsoft-forums.uk/account/signature
But we seem to lack the permissions to do that, which for XenForo usually means its either not been enabled in ACP or the maximum character count is still set at 0, which defacto disables it.