20" Lawn Mower battery not holding up

I used my lawn mower last year with no problem. However, this was in mid-July when the grass was more brittle.

I've now been cutting the grass for the last month and a half and I am not happy with the battery life. I had to raise the blade to the highest setting in order to keep the green light on. However, even then, I would get an orange light often. What's the deal with that?

I last cut my grass on Sunday (at the highest setting) and did it again today (Wednesday) on the middle setting. I continued to get an orange light and my battery died after only getting done with my front yard. Last year, I was able to complete the front and most of the back yard in 1 battery life. I had to switch to my smaller weed whacked battery, but that only lasted a few passes too! I then had to wait for the big battery to charge in order to finish the job!

I'm wondering if I'm doing something wrong or if it's just because of the season? Is it because I'm mulching it instead of bagging it? Would it make a difference if I bagged it? Either way, I'm annoyed!!