Work Van Owner's - how long does the typical battery last?

[ea90gl]

Hi fellas, I just wanted to hear from the work van owners out there in regards to what sort of lifespan that they have gotten out of the batteries in their work vehicles.

The reason for asking is I currently own a 11 month work van (bought new and now has 19,500km). Approximately 6 months into ownership the battery went flat (with no warning at all and with minimal stationary power usage) however after waiting about 20mins it just got started again and away I went. Due to the flat battery the vehicle was displaying an error message which I had road-side assist attend to just to cover my tracks. Eventually after some more driving the error message disappeared most likely due to the proper charge up.

Only earlier this evening the battery packed up again however this time it was a complete no go, it just ticked over. Again comes roadside assist to replace the battery however he mentioned "it passed the test however I will still replace it to save you the headache". Long story short the replacement battery is physically smaller so some dodgy works have been put in place to stop it from sliding and the assistant dropped and lost the battery clamp bolt which means there currently is no clamp in place. He assured me he will get in touch with me ASAP to rectify the issue and finalise the paperworks.

This battery life to me seems very unusual (regardless of it being a commercial vehicle) and I am assuming the battery is a dud and must come under the 12 month battery warranty. I do not leave on interior lights, crank the radio for hours on end constantly and always disable the start/stop feature when driving (whether or not the battery has anything to do with this I am not sure of). Stop/start driving makes up at least 40% of my driving which I do not personally see as excessive). The van has no aftermarket accessories at all which would put any additional strain on the battery. Yes I do open and close the doors often while working which operate the interior lights excessively however even still this can surely not wear out the battery so quick.

As mentioned I would love to hear from any one relating to the above. Thanks in advance