Agree anything less than 12"x12"x12" dimensions or flat rate box will be cheaper using USPS. The issue with these batteries for shipping is the Dangerous Goods classification. USPS has a very limited list of accepted Dangerous Goods.
Shipping costs can be a frustration for sure. I always remember a great tip I got when I was just getting into selling online... "the fastest way to go broke in business is with shipping...". We had been discussing whether to offer free shipping as well as underestimating cost...so, no worries about shipping cost to me if/when you get more cells. That's factored into my view of the price.Hope to have them all shipped this week I'm just working on other shipping options UPS wants $33.00 per cell. My budget was $15 but I will still cover the cost no matter the amount.
I eventually moved
to using http://www.Endicia.com for postage. They used to offer slightly lower postage rates and so-so insurance rates. I changed to using either http://www.u-pic.com to cover all my shipments. There is also PIPINSURE.COM for parcel insurance.
The change to 3rd party parcel insurance actually turned shipping charges into a profit center as I still charged for insurance in the shipping rates from USPS when calculating shipping charges. It's a shockingly significant difference over a year.