1800mAh won't probably make that much of a difference for Optimus. Optimus has one of the largest batteries for a phone of its kind. 1500mAh itself is pretty high capacity.
I really don't think the extra 45$ is worth the extra 300mAh. You are better off buying an external portable charger. They run at around 20-30$. You could probably get an excellent one for 45$.
For example, this one here,
has a 5000mAh battery.
Just get any portable USB charger.