It's hard to say without knowing the exact thermo, but I'll be honest, Chris - as important as it is to the process, I just replace. I love the Thermoworks RTC 600C (same company that makes the Thermopen, only cheaper). Less than $20 on Amazon. I've been through a couple of them in the last years. Just my $0.02. .
Thanks Jon! Just purchased a replacement on Amazon that takes one aaa battery which should simplify matters in the future.