Run time for brush cutter on 2.5ah battery

I've had the 15 string trimmer with a 2.5ah battery for just under 2years now, and it has really good run time, same as documented 45min.  

This product made me a big fan of EGO. 

I decided to expand my EGO set by getting the power head + pole saw + hedge kit which comes with a 2.5ah battery, and also got the brush cutter attachment. At time of purchase I confirmed run time for the brush cutter on 2.5ah as 27min which was low but ok as I have 2 other 2.5ah batteries.

I tested the brush cutter using the new and old(er) 2.5ah batteries and even on very low load, cutting 6" grass on a slope not accessible by my mower the powerhead+brush cutter would do the following:
- battery 1 stops after 2min with battery is flashing orange
- switch to battery 2, and same result after 2min, flashing orange
- switch back to battery 1, get 7-9min run time before flashing red
- battery 1 stops after 2-3min more run time then full red
- switch to battery 2, same result 7min till flashing red, then 2min to full red

So there are 2 problems here:
1) the full run time is only ~ 12min with very load load and moderate temp (advertised as 27min)
2) the initial stop with orange flashing


Settup / Enviromental:
- power head speed = 2
- Temperature for tests was 17degC / 63degF. 
- grass being cut is 6" tall hollow mounds of grass, very low load. This is hard to explain, the lumps of grass are from having horses, and the grass grows over their waste, but becomes hollow.