It has no agro range as it isn't a true pet - it cannot be attacked or even targeted.
It follows you around (rather tacky) and it only fires one attack, Charged Bolts (does it at Corruptor scale, with Scourge). The recharge timer on the attack is 2.5s, and is not affected by Hasten or SB, but it benefits from any RchgRedux enhancements that you slot into it!
I've found that it attacks once it's withing 45" of an enemy that is closest to it.
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(does it at Corruptor scale, with Scourge)
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Yup.
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... it benefits from any RchgRedux enhancements that you slot into it!
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Do you mean to say that it benefits from RechRdx in the obvious way i.e by increasing the Rechg of the power, or do you mean that slotting Rechg will actually increase the sentinals attack rate? 
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... it benefits from any RchgRedux enhancements that you slot into it!
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Do you mean to say that it benefits from RechRdx in the obvious way i.e by increasing the Rechg of the power, or do you mean that slotting Rechg will actually increase the sentinals attack rate?
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Both, I think. So a RechRdx will both recharge the power to you and increase the Volt's firing rate 
Awesome! In that case my plan is to slot it with a Soulbound Allegiance "Chance For Build Up" , and whack a couple of rechgs to increase the hit rate of the buff. Use sparky as a build up monkey
ive just reached lvl 38 with my Mind/elec dom...but everyone says to me that voltaic sentinel is not worth taking. Mainly because of the short duration of 1min. But the damage doesnt seem to be too bad at all.
So what should i do now? take it if i got nothing better or avoid it at all circumstances?
BANG BANG!!!
Short duration? It's equal to the recharge (60 seconds). It's perma, unenhanced. And you can't have more than one out at the same time anyway. Why does the recharge matter at all, in this case?
because its annoying...
BANG BANG!!!
Ive tried voltaic sentinel yesterday, the damage seems to be ok. But as i already thought, resummon it every minute is very annoying. The duration should be 3min, otherwise its very importunate (and end heavy).
BANG BANG!!!
How does the Voltaic Sentinel work, compared to the normal dominator pet. Say Singularity?
I know it only last one minute, but if it works like my experience with Singularity (tend to hang back and have a short argo range) it would not sound that useful to me.