To me it feels most useful to invest the attributes like that:
1st) As much as needed in memory. Bar compression is important, sort out skills you don't really need or which you only use every now and then and might even substitute with scrolls, grenades etc.; that allows you to invest more into attributes increasing your damage.
2nd) Everything else into your damage attribute.
3rd) If you hit the maximum investment for your damage attribute, put some points into Wits.
Whether you want to increase your strength or intelligence attribute depends on how you want to equip your battle mage, that is: How you want to design your whole team build. As far as I know most people try to avoid splitting their team's damage in both magic and physical damage as that means you'll have to either destroy both armor types on each foe or split your damage up in the first place, not focusing the same foe with all/most toons in your team. Battle mages are in a somewhat odd position as they're designed to combine both a magic and physical approach which will probably lead to ineffectivity. Some options are:
A) Wield a staff and put all attribute points into Intelligence. Staves deal elemental damage, so their damage is increased by Intelligence. Only use as many skill points on Warfare as you need. Usually Warfare is the best skill to invest points in for increasing your damage, but it does only count for physical damage. Therefore Increasing warfare will not increase your damage output while wielding a staff.
Equipping yourself like that will result in only damaging the opponent's magic armor with both skills and magic, which leads to a relatively quick possibility to apply status effects such as blind, shocked, stunned, burning. The downside is that your special weapon attacks performed with the staff won't be able to inflict physical based status effects such as crippled or knocked down, given you don't touch their physical armor which will make them resist the physical based status effects.
After you spent all points needed for your skills of desire start investing into polymorph and spend the additional attribute points into Intelligence. This will increase the damage of your staff attacks and spells from almost every school of magic.
This approach should combine well with a team featuring mostly mages.
B) Wield martial weapons and put points both in strength (finesse if using a spear or daggers) and intelligence. You will have to decrease both physical and magic armor on your foes in order to kill them or apply status effects. Sounds quite ineffective. Maybe if played with a mixed physical and magic team usally focusing the same target ... :s
C) Wield martial weapons and put points in strength (or finesse if using a spear or daggers) only. In this case, don't understand a battle mage as a person which uses its magic to directly damage foes – your magic damage output will be really low. You would go for warfare + any magic elemental skill and use that skill pool for support and utility skills only. Else, try the Inquisitor preset combining the physical damage and support based necromancy skill pool.
This approach combines best with a full physical team.
I hope this might be helpful for you. You should wait for some more people replying as they'll probably add and correct some info.
